diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Interfaces/Repositories/ISecuredWriteRepository.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Interfaces/Repositories/ISecuredWriteRepository.cs
index f2247f59..d7f35b11 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Commons/Interfaces/Repositories/ISecuredWriteRepository.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Interfaces/Repositories/ISecuredWriteRepository.cs
@@ -54,4 +54,29 @@ public interface ISecuredWriteRepository
         int skip,
         int take,
         CancellationToken ct = default);
+
+    /// <summary>
+    /// Atomically flips a row from <c>Pending</c> to <c>Approved</c>, stamping the
+    /// verifier identity, comment, and decision time, but ONLY if the row is still
+    /// <c>Pending</c>. This is the compare-and-swap guard for the two-verifier race
+    /// (M7 / T14b): two verifiers may approve the same write concurrently, but the
+    /// conditional <c>WHERE Status='Pending'</c> guarantees exactly one wins. The
+    /// loser observes <c>false</c> and must not relay the write.
+    /// </summary>
+    /// <param name="id">Identity of the pending secured write.</param>
+    /// <param name="verifierUser">The approving verifier's username.</param>
+    /// <param name="verifierComment">Optional free-text comment from the verifier.</param>
+    /// <param name="decidedAtUtc">UTC instant the approval decision was made.</param>
+    /// <param name="ct">Cancellation token.</param>
+    /// <returns>
+    /// A task resolving to <c>true</c> if this caller won the approval (exactly one
+    /// row transitioned), or <c>false</c> if the row was no longer <c>Pending</c>
+    /// (already decided by another verifier).
+    /// </returns>
+    Task<bool> TryMarkApprovedAsync(
+        long id,
+        string verifierUser,
+        string? verifierComment,
+        DateTime decidedAtUtc,
+        CancellationToken ct = default);
 }
diff --git a/src/ZB.MOM.WW.ScadaBridge.Communication/CommunicationService.cs b/src/ZB.MOM.WW.ScadaBridge.Communication/CommunicationService.cs
index b80f627e..b78da1af 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Communication/CommunicationService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Communication/CommunicationService.cs
@@ -3,6 +3,7 @@ using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.Artifacts;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.Audit;
+using ZB.MOM.WW.ScadaBridge.Commons.Messages.DataConnection;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.DebugView;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.Deployment;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.Health;
@@ -417,6 +418,33 @@ public class CommunicationService
             envelope, _options.QueryTimeout, cancellationToken);
     }
 
+    // ── Secured Write Relay (M7 / T14b — approve → site MxGateway write) ──
+
+    /// <summary>
+    /// Relays a single tag write to the site's data connection and awaits the
+    /// outcome. Used by the secured-write (two-person) approve flow: once a
+    /// Verifier's approval wins the compare-and-swap, the central ManagementActor
+    /// calls this to execute the write against the site's MxGateway connection.
+    /// The request is the existing <see cref="WriteTagRequest"/>, already handled
+    /// site-side by <c>DataConnectionActor</c> (routed to the MxGateway adapter) —
+    /// no site-side change is required. The Ask is bounded by
+    /// <see cref="CommunicationOptions.QueryTimeout"/>, mirroring
+    /// <see cref="BrowseNodeAsync"/> and the other one-shot site queries.
+    /// </summary>
+    /// <param name="siteId">The target site identifier.</param>
+    /// <param name="request">The tag write request (correlation id + connection + tag + value + timestamp).</param>
+    /// <param name="ct">Cancellation token.</param>
+    /// <returns>The write response (success flag + optional error message).</returns>
+    public virtual Task<WriteTagResponse> WriteTagAsync(
+        string siteId,
+        WriteTagRequest request,
+        CancellationToken ct = default)
+    {
+        var envelope = new SiteEnvelope(siteId, request);
+        return GetActor().Ask<WriteTagResponse>(
+            envelope, _options.QueryTimeout, ct);
+    }
+
     // ── Pattern 8: Heartbeat (site→central, Tell) ──
     // Heartbeats are received by central, not sent. No method needed here.
 
diff --git a/src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/SecuredWriteRepository.cs b/src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/SecuredWriteRepository.cs
index 5fa53fe0..cc34852b 100644
--- a/src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/SecuredWriteRepository.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/SecuredWriteRepository.cs
@@ -79,4 +79,31 @@ public class SecuredWriteRepository : ISecuredWriteRepository
             .Take(take)
             .ToListAsync(ct);
     }
+
+    /// <inheritdoc />
+    public async Task<bool> TryMarkApprovedAsync(
+        long id,
+        string verifierUser,
+        string? verifierComment,
+        DateTime decidedAtUtc,
+        CancellationToken ct = default)
+    {
+        // Single-statement compare-and-swap: the conditional WHERE Status='Pending'
+        // makes the Pending->Approved transition atomic at the row level, so two
+        // verifiers approving concurrently produce exactly one rowsAffected==1 (the
+        // winner) and one rowsAffected==0 (the loser). Parameterised via
+        // ExecuteSqlInterpolatedAsync — same raw-SQL conditional-update pattern as
+        // SiteCallAuditRepository's upsert-on-newer-status path.
+        var rowsAffected = await _context.Database.ExecuteSqlInterpolatedAsync(
+            $@"UPDATE dbo.PendingSecuredWrites
+SET Status = 'Approved',
+    VerifierUser = {verifierUser},
+    VerifierComment = {verifierComment},
+    DecidedAtUtc = {decidedAtUtc}
+WHERE Id = {id}
+  AND Status = 'Pending';",
+            ct);
+
+        return rowsAffected == 1;
+    }
 }
diff --git a/src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs b/src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs
index 8ef7e113..5a1db8db 100644
--- a/src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs
@@ -378,10 +378,11 @@ public class ManagementActor : ReceiveActor
             DiscardParkedMessageCommand cmd => await HandleDiscardParkedMessage(sp, cmd, user),
             DebugSnapshotCommand cmd => await HandleDebugSnapshot(sp, cmd, user),
 
-            // Secured writes (M7 / T14b). Approve (execute) is intentionally NOT
-            // dispatched here — the approve->execute relay is Task C3; it would
-            // 'NotSupported' at runtime until then.
+            // Secured writes (M7 / T14b). Approve executes the write — once a
+            // Verifier wins the compare-and-swap the value is relayed to the site
+            // MxGateway connection (Task C3).
             SubmitSecuredWriteCommand cmd => await HandleSubmitSecuredWrite(sp, cmd, user),
+            ApproveSecuredWriteCommand cmd => await HandleApproveSecuredWrite(sp, cmd, user),
             RejectSecuredWriteCommand cmd => await HandleRejectSecuredWrite(sp, cmd, user),
             ListSecuredWritesCommand cmd => await HandleListSecuredWrites(sp, cmd),
 
@@ -928,6 +929,87 @@ public class ManagementActor : ReceiveActor
         return ToSecuredWriteDto(entity);
     }
 
+    private static async Task<object?> HandleApproveSecuredWrite(
+        IServiceProvider sp, ApproveSecuredWriteCommand cmd, AuthenticatedUser user)
+    {
+        var repo = sp.GetRequiredService<ISecuredWriteRepository>();
+        var row = await repo.GetAsync(cmd.Id)
+            ?? throw new ManagementCommandException($"Secured write {cmd.Id} not found.");
+
+        if (!string.Equals(row.Status, "Pending", StringComparison.Ordinal))
+            throw new ManagementCommandException(
+                $"Secured write {cmd.Id} is '{row.Status}', not Pending; it cannot be approved.");
+
+        // Separation of duties: a write may not be verified by its submitter. Checked
+        // BEFORE the CAS so a self-approval never consumes the Pending->Approved
+        // transition.
+        if (string.Equals(row.OperatorUser, user.Username, StringComparison.OrdinalIgnoreCase))
+            throw new ManagementCommandException(
+                "A secured write cannot be verified by its submitter.");
+
+        // Compare-and-swap: guards the two-verifier race. Exactly one concurrent
+        // approver flips Pending->Approved; the loser observes false here and must
+        // not relay the write.
+        var decidedAtUtc = DateTime.UtcNow;
+        if (!await repo.TryMarkApprovedAsync(cmd.Id, user.Username, cmd.Comment, decidedAtUtc))
+            throw new ManagementCommandException(
+                $"Secured write {cmd.Id} is no longer pending — already decided.");
+
+        // We won the race. Stamp the verifier decision locally so the entity we
+        // persist below carries the same values the CAS committed.
+        row.Status = "Approved";
+        row.VerifierUser = user.Username;
+        row.VerifierComment = cmd.Comment;
+        row.DecidedAtUtc = decidedAtUtc;
+
+        // Validate the value type BEFORE attempting the relay. An unknown type can
+        // never be decoded/written, so fail the row deterministically rather than
+        // leaving it stuck Approved. (Addresses the C2 reviewer's deferred
+        // ValueType-validation note.)
+        if (!Enum.TryParse<Commons.Types.Enums.DataType>(row.ValueType, ignoreCase: true, out var dataType))
+        {
+            row.Status = "Failed";
+            row.ExecutedAtUtc = DateTime.UtcNow;
+            row.ExecutionError = "unknown value type";
+            await repo.UpdateAsync(row);
+            return ToSecuredWriteDto(row);
+        }
+
+        var value = Commons.Types.AttributeValueCodec.Decode(row.ValueJson, dataType, elementType: null);
+
+        // Relay the write to the site MxGateway connection. A transport exception is
+        // contained so the row is never left stuck Approved.
+        var commService = sp.GetRequiredService<CommunicationService>();
+        bool success;
+        string? error;
+        try
+        {
+            var resp = await commService.WriteTagAsync(
+                row.SiteId,
+                new Commons.Messages.DataConnection.WriteTagRequest(
+                    CorrelationId: Guid.NewGuid().ToString("N"),
+                    ConnectionName: row.ConnectionName,
+                    TagPath: row.TagPath,
+                    Value: value,
+                    Timestamp: DateTimeOffset.UtcNow));
+            success = resp.Success;
+            error = resp.Success ? null : resp.ErrorMessage;
+        }
+        catch (Exception ex)
+        {
+            success = false;
+            error = ex.Message;
+        }
+
+        row.Status = success ? "Executed" : "Failed";
+        row.ExecutedAtUtc = DateTime.UtcNow;
+        row.ExecutionError = error;
+
+        // UpdateAsync overwrites all columns -> pass the fully-populated entity.
+        await repo.UpdateAsync(row);
+        return ToSecuredWriteDto(row);
+    }
+
     private static async Task<object?> HandleRejectSecuredWrite(
         IServiceProvider sp, RejectSecuredWriteCommand cmd, AuthenticatedUser user)
     {
diff --git a/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/SecuredWriteHandlerTests.cs b/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/SecuredWriteHandlerTests.cs
index aa30bda8..d9065278 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/SecuredWriteHandlerTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/SecuredWriteHandlerTests.cs
@@ -2,12 +2,15 @@ using Akka.Actor;
 using Akka.TestKit.Xunit2;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
 using NSubstitute;
 using ZB.MOM.WW.ScadaBridge.Commons.Entities.SecuredWrites;
 using ZB.MOM.WW.ScadaBridge.Commons.Entities.Sites;
 using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
+using ZB.MOM.WW.ScadaBridge.Commons.Messages.DataConnection;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.Management;
 using ZB.MOM.WW.ScadaBridge.Commons.Types;
+using ZB.MOM.WW.ScadaBridge.Communication;
 
 namespace ZB.MOM.WW.ScadaBridge.ManagementService.Tests;
 
@@ -21,16 +24,54 @@ public class SecuredWriteHandlerTests : TestKit, IDisposable
 {
     private readonly ISiteRepository _siteRepo;
     private readonly ISecuredWriteRepository _securedWriteRepo;
+    private readonly StubCommunicationService _comms;
     private readonly ServiceCollection _services;
 
     public SecuredWriteHandlerTests()
     {
         _siteRepo = Substitute.For<ISiteRepository>();
         _securedWriteRepo = Substitute.For<ISecuredWriteRepository>();
+        _comms = new StubCommunicationService();
 
         _services = new ServiceCollection();
         _services.AddScoped(_ => _siteRepo);
         _services.AddScoped(_ => _securedWriteRepo);
+        _services.AddSingleton<CommunicationService>(_comms);
+    }
+
+    /// <summary>
+    /// Test double for the site-write seam. <see cref="CommunicationService.WriteTagAsync"/>
+    /// is virtual so the approve relay can be exercised without a live actor system;
+    /// records the relayed request and returns a canned response.
+    /// </summary>
+    private sealed class StubCommunicationService : CommunicationService
+    {
+        public StubCommunicationService()
+            : base(Options.Create(new CommunicationOptions()), NullLogger<CommunicationService>.Instance)
+        {
+        }
+
+        public WriteTagRequest? LastRequest { get; private set; }
+
+        public int CallCount { get; private set; }
+
+        public Func<WriteTagRequest, WriteTagResponse> Responder { get; set; } =
+            req => new WriteTagResponse(req.CorrelationId, Success: true, ErrorMessage: null, DateTimeOffset.UtcNow);
+
+        public Exception? ThrowOnWrite { get; set; }
+
+        public override Task<WriteTagResponse> WriteTagAsync(
+            string siteId, WriteTagRequest request, CancellationToken ct = default)
+        {
+            CallCount++;
+            LastRequest = request;
+            if (ThrowOnWrite is not null)
+            {
+                return Task.FromException<WriteTagResponse>(ThrowOnWrite);
+            }
+
+            return Task.FromResult(Responder(request));
+        }
     }
 
     private IActorRef CreateActor()
@@ -270,4 +311,160 @@ public class SecuredWriteHandlerTests : TestKit, IDisposable
         ExpectMsg<ManagementSuccess>(TimeSpan.FromSeconds(5));
         _securedWriteRepo.Received(1).QueryAsync(null, null, 0, 200, Arg.Any<CancellationToken>());
     }
+
+    // ------------------------------------------------------------------------
+    // Approve (execute) — Task C3
+    // ------------------------------------------------------------------------
+
+    /// <summary>Arms the CAS to succeed (a different verifier wins the race).</summary>
+    private void ArmCasSuccess(long id) =>
+        _securedWriteRepo.TryMarkApprovedAsync(
+                id, Arg.Any<string>(), Arg.Any<string?>(), Arg.Any<DateTime>(), Arg.Any<CancellationToken>())
+            .Returns(true);
+
+    [Fact]
+    public void Approve_ByDifferentVerifier_RelaysWrite_FlipsStatusToExecuted()
+    {
+        SeedPendingWrite(7, operatorUser: "alice");
+        ArmCasSuccess(7);
+
+        PendingSecuredWrite? updated = null;
+        _securedWriteRepo
+            .When(r => r.UpdateAsync(Arg.Any<PendingSecuredWrite>(), Arg.Any<CancellationToken>()))
+            .Do(ci => updated = ci.Arg<PendingSecuredWrite>());
+
+        var actor = CreateActor();
+        var envelope = Envelope(new ApproveSecuredWriteCommand(7, "approved"), "bob", "Verifier");
+
+        actor.Tell(envelope);
+
+        var response = ExpectMsg<ManagementSuccess>(TimeSpan.FromSeconds(5));
+        Assert.Equal(envelope.CorrelationId, response.CorrelationId);
+
+        // The CAS guarded the transition (exactly once).
+        _securedWriteRepo.Received(1).TryMarkApprovedAsync(
+            7, "bob", "approved", Arg.Any<DateTime>(), Arg.Any<CancellationToken>());
+
+        // The write was relayed to the site MxGateway connection.
+        Assert.Equal(1, _comms.CallCount);
+        Assert.NotNull(_comms.LastRequest);
+        Assert.Equal("Mx1", _comms.LastRequest!.ConnectionName);
+        Assert.Equal("Tag.A", _comms.LastRequest.TagPath);
+
+        Assert.NotNull(updated);
+        Assert.Equal("Executed", updated!.Status);
+        Assert.NotNull(updated.ExecutedAtUtc);
+        Assert.Null(updated.ExecutionError);
+    }
+
+    [Fact]
+    public void Approve_BySubmittingUser_ReturnsError_CasNotCalled_NoRelay()
+    {
+        SeedPendingWrite(7, operatorUser: "alice");
+
+        var actor = CreateActor();
+        // Same principal that submitted attempts to approve — separation of duties.
+        var envelope = Envelope(new ApproveSecuredWriteCommand(7, "self"), "alice", "Verifier");
+
+        actor.Tell(envelope);
+
+        var response = ExpectMsg<ManagementError>(TimeSpan.FromSeconds(5));
+        Assert.Equal("COMMAND_FAILED", response.ErrorCode);
+        _securedWriteRepo.DidNotReceiveWithAnyArgs().TryMarkApprovedAsync(
+            default, default!, default, default, default);
+        Assert.Equal(0, _comms.CallCount);
+    }
+
+    [Fact]
+    public void Approve_WhenCasLosesRace_ReturnsError_NoRelay()
+    {
+        SeedPendingWrite(7, operatorUser: "alice");
+        _securedWriteRepo.TryMarkApprovedAsync(
+                7, Arg.Any<string>(), Arg.Any<string?>(), Arg.Any<DateTime>(), Arg.Any<CancellationToken>())
+            .Returns(false);
+
+        var actor = CreateActor();
+        var envelope = Envelope(new ApproveSecuredWriteCommand(7, "race"), "bob", "Verifier");
+
+        actor.Tell(envelope);
+
+        var response = ExpectMsg<ManagementError>(TimeSpan.FromSeconds(5));
+        Assert.Equal("COMMAND_FAILED", response.ErrorCode);
+        Assert.Contains("already decided", response.Error);
+        Assert.Equal(0, _comms.CallCount);
+    }
+
+    [Fact]
+    public void Approve_WhenRelayFails_FlipsStatusToFailed_WithError()
+    {
+        SeedPendingWrite(7, operatorUser: "alice");
+        ArmCasSuccess(7);
+        _comms.Responder = req =>
+            new WriteTagResponse(req.CorrelationId, Success: false, ErrorMessage: "device offline", DateTimeOffset.UtcNow);
+
+        PendingSecuredWrite? updated = null;
+        _securedWriteRepo
+            .When(r => r.UpdateAsync(Arg.Any<PendingSecuredWrite>(), Arg.Any<CancellationToken>()))
+            .Do(ci => updated = ci.Arg<PendingSecuredWrite>());
+
+        var actor = CreateActor();
+        var envelope = Envelope(new ApproveSecuredWriteCommand(7, "approved"), "bob", "Verifier");
+
+        actor.Tell(envelope);
+
+        // The approve itself succeeds (the row was decided); the relay outcome is recorded on the row.
+        ExpectMsg<ManagementSuccess>(TimeSpan.FromSeconds(5));
+        Assert.Equal(1, _comms.CallCount);
+        Assert.NotNull(updated);
+        Assert.Equal("Failed", updated!.Status);
+        Assert.Equal("device offline", updated.ExecutionError);
+        Assert.NotNull(updated.ExecutedAtUtc);
+    }
+
+    [Fact]
+    public void Approve_WhenRelayThrows_FlipsStatusToFailed_WithExceptionMessage()
+    {
+        SeedPendingWrite(7, operatorUser: "alice");
+        ArmCasSuccess(7);
+        _comms.ThrowOnWrite = new InvalidOperationException("transport down");
+
+        PendingSecuredWrite? updated = null;
+        _securedWriteRepo
+            .When(r => r.UpdateAsync(Arg.Any<PendingSecuredWrite>(), Arg.Any<CancellationToken>()))
+            .Do(ci => updated = ci.Arg<PendingSecuredWrite>());
+
+        var actor = CreateActor();
+        var envelope = Envelope(new ApproveSecuredWriteCommand(7, "approved"), "bob", "Verifier");
+
+        actor.Tell(envelope);
+
+        ExpectMsg<ManagementSuccess>(TimeSpan.FromSeconds(5));
+        Assert.NotNull(updated);
+        Assert.Equal("Failed", updated!.Status);
+        Assert.Contains("transport down", updated.ExecutionError);
+    }
+
+    [Fact]
+    public void Approve_UnknownValueType_FlipsStatusToFailed_NoRelay()
+    {
+        var row = SeedPendingWrite(7, operatorUser: "alice");
+        row.ValueType = "Bogus";
+        ArmCasSuccess(7);
+
+        PendingSecuredWrite? updated = null;
+        _securedWriteRepo
+            .When(r => r.UpdateAsync(Arg.Any<PendingSecuredWrite>(), Arg.Any<CancellationToken>()))
+            .Do(ci => updated = ci.Arg<PendingSecuredWrite>());
+
+        var actor = CreateActor();
+        var envelope = Envelope(new ApproveSecuredWriteCommand(7, "approved"), "bob", "Verifier");
+
+        actor.Tell(envelope);
+
+        ExpectMsg<ManagementSuccess>(TimeSpan.FromSeconds(5));
+        Assert.Equal(0, _comms.CallCount);
+        Assert.NotNull(updated);
+        Assert.Equal("Failed", updated!.Status);
+        Assert.Equal("unknown value type", updated.ExecutionError);
+    }
 }