diff --git a/src/Cli.Tests/CustomLoggerTests.cs b/src/Cli.Tests/CustomLoggerTests.cs
index cce73f0f75..7d66839e58 100644
--- a/src/Cli.Tests/CustomLoggerTests.cs
+++ b/src/Cli.Tests/CustomLoggerTests.cs
@@ -1,6 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using System.Text.RegularExpressions;
+
 namespace Cli.Tests;
 
 /// <summary>
@@ -77,8 +79,9 @@ public void LogOutput_UsesAbbreviatedLogLevelLabels(LogLevel logLevel, string ex
         string actual = expectStderr ? stderr : stdout;
         string other = expectStderr ? stdout : stderr;
 
-        Assert.IsTrue(actual.StartsWith(expectedPrefix),
-            $"Expected output to start with '{expectedPrefix}' but got: '{actual}'");
+        Assert.IsTrue(
+            Regex.IsMatch(actual, $@"^\d{{4}}-\d{{2}}-\d{{2}}T\d{{2}}:\d{{2}}:\d{{2}}\.\d{{3}}Z {Regex.Escape(expectedPrefix)}"),
+            $"Expected output to start with an ISO 8601 UTC timestamp followed by '{expectedPrefix}' but got: '{actual}'");
         StringAssert.Contains(actual, Message);
         Assert.AreEqual(string.Empty, other,
             $"Did not expect output on the other stream but got: '{other}'");
diff --git a/src/Cli/CustomLoggerProvider.cs b/src/Cli/CustomLoggerProvider.cs
index a4625b0924..532cd74f2c 100644
--- a/src/Cli/CustomLoggerProvider.cs
+++ b/src/Cli/CustomLoggerProvider.cs
@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using System.Globalization;
 using Microsoft.Extensions.Logging;
 
 /// <summary>
@@ -25,6 +26,8 @@ public ILogger CreateLogger(string categoryName)
 
     public class CustomConsoleLogger : ILogger
     {
+        private const string UTC_TIMESTAMP_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.fff'Z'";
+
         private readonly LogLevel _minimumLogLevel;
 
         // Minimum LogLevel for CLI output.
@@ -124,13 +127,14 @@ public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Except
                 // Apply colors so the abbreviation matches the visual style of engine logs.
                 // try/finally guarantees the original colors are restored even if Write throws,
                 // otherwise the console would be left tinted (e.g. red on error) for subsequent output.
+                string mcpTimestamp = DateTime.UtcNow.ToString(UTC_TIMESTAMP_FORMAT, CultureInfo.InvariantCulture);
                 ConsoleColor mcpOriginalForeGroundColor = Console.ForegroundColor;
                 ConsoleColor mcpOriginalBackGroundColor = Console.BackgroundColor;
                 try
                 {
                     Console.ForegroundColor = _logLevelToForeGroundConsoleColorMap.GetValueOrDefault(logLevel, ConsoleColor.White);
                     Console.BackgroundColor = _logLevelToBackGroundConsoleColorMap.GetValueOrDefault(logLevel, ConsoleColor.Black);
-                    Console.Error.Write($"{mcpAbbreviation}:");
+                    Console.Error.Write($"{mcpTimestamp} {mcpAbbreviation}:");
                 }
                 finally
                 {
@@ -153,6 +157,7 @@ public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Except
             }
 
             TextWriter writer = logLevel >= LogLevel.Error ? Console.Error : Console.Out;
+            string timestamp = DateTime.UtcNow.ToString(UTC_TIMESTAMP_FORMAT, CultureInfo.InvariantCulture);
             // try/finally guarantees the original colors are restored even if Write throws,
             // otherwise the console would be left tinted (e.g. red on error) for subsequent output.
             ConsoleColor originalForeGroundColor = Console.ForegroundColor;
@@ -161,7 +166,7 @@ public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Except
             {
                 Console.ForegroundColor = _logLevelToForeGroundConsoleColorMap.GetValueOrDefault(logLevel, ConsoleColor.White);
                 Console.BackgroundColor = _logLevelToBackGroundConsoleColorMap.GetValueOrDefault(logLevel, ConsoleColor.Black);
-                writer.Write($"{abbreviation}:");
+                writer.Write($"{timestamp} {abbreviation}:");
             }
             finally
             {
diff --git a/src/Service/Program.cs b/src/Service/Program.cs
index 76af52ba97..ca7186698d 100644
--- a/src/Service/Program.cs
+++ b/src/Service/Program.cs
@@ -26,6 +26,7 @@
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.ApplicationInsights;
+using Microsoft.Extensions.Logging.Console;
 using OpenTelemetry.Exporter;
 using OpenTelemetry.Logs;
 using OpenTelemetry.Resources;
@@ -194,6 +195,11 @@ public static IHostBuilder CreateHostBuilder(string[] args, bool runMcpStdio, st
                     else
                     {
                         logging.SetMinimumLevel(LogLevelProvider.CurrentLogLevel);
+                        logging.Services.Configure<SimpleConsoleFormatterOptions>(options =>
+                        {
+                            options.TimestampFormat = "yyyy-MM-dd'T'HH:mm:ss.fff'Z' ";
+                            options.UseUtcTimestamp = true;
+                        });
                     }
 
                     // Add filter for dynamic log level changes (e.g., via MCP logging/setLevel)
@@ -464,7 +470,14 @@ public static ILoggerFactory GetLoggerFactoryForLogLevel(
                         // When LogLevel.None, skip the console logger entirely for true silence.
                         if (LogLevelProvider.CurrentLogLevel != LogLevel.None)
                         {
-                            builder.AddConsole(options =>
+                            builder.AddSimpleConsole(options =>
+                            {
+                                options.TimestampFormat = "yyyy-MM-dd'T'HH:mm:ss.fff'Z' ";
+                                options.UseUtcTimestamp = true;
+                            });
+                            // Route all levels to stderr to keep stdout clean for MCP JSON-RPC.
+                            // Uses Services.Configure (not AddConsole) so no second provider is registered.
+                            builder.Services.Configure<ConsoleLoggerOptions>(options =>
                             {
                                 options.LogToStandardErrorThreshold = LogLevel.Trace;
                             });
@@ -472,7 +485,11 @@ public static ILoggerFactory GetLoggerFactoryForLogLevel(
                     }
                     else
                     {
-                        builder.AddConsole();
+                        builder.AddSimpleConsole(options =>
+                        {
+                            options.TimestampFormat = "yyyy-MM-dd'T'HH:mm:ss.fff'Z' ";
+                            options.UseUtcTimestamp = true;
+                        });
                     }
                 });
         }