diff --git a/src/TeamsISO.App/Themes/WildDragonTheme.xaml b/src/TeamsISO.App/Themes/WildDragonTheme.xaml
index 48f2f2a..7bb6914 100644
--- a/src/TeamsISO.App/Themes/WildDragonTheme.xaml
+++ b/src/TeamsISO.App/Themes/WildDragonTheme.xaml
@@ -740,6 +740,15 @@
             <Trigger Property="IsSelected" Value="True">
                 <Setter Property="Background" Value="{StaticResource Wd.SurfaceElevated}"/>
             </Trigger>
+            <!-- Active speaker highlight: set by MainViewModel at the 1Hz
+                 stats tick based on DisplayedAudioLevel. Cyan left border
+                 (3px) makes whoever's talking pop without changing the
+                 background color (which IsMouseOver / IsSelected own). -->
+            <DataTrigger Binding="{Binding IsActiveSpeaker}" Value="True">
+                <Setter Property="BorderBrush" Value="{StaticResource Wd.Accent.Cyan}"/>
+                <Setter Property="BorderThickness" Value="3,0,0,1"/>
+                <Setter Property="Background" Value="{StaticResource Wd.Accent.CyanMuted}"/>
+            </DataTrigger>
         </Style.Triggers>
     </Style>
 
diff --git a/src/TeamsISO.App/ViewModels/MainViewModel.cs b/src/TeamsISO.App/ViewModels/MainViewModel.cs
index c721abb..8183311 100644
--- a/src/TeamsISO.App/ViewModels/MainViewModel.cs
+++ b/src/TeamsISO.App/ViewModels/MainViewModel.cs
@@ -752,6 +752,29 @@ public sealed class MainViewModel : ObservableObject, IDisposable
             }
         }
 
+        // Active-speaker highlight: find the loudest enabled participant
+        // and mark their IsActiveSpeaker flag. Only one row at a time;
+        // ties broken by enumeration order (first one wins). Threshold of
+        // 0.05 prevents constant flicker between near-silent participants
+        // when nobody's really speaking.
+        ParticipantViewModel? loudest = null;
+        double loudestLevel = 0.05;
+        foreach (var p in Participants)
+        {
+            if (!p.IsEnabled) continue;
+            if (p.DisplayedAudioLevel > loudestLevel)
+            {
+                loudest = p;
+                loudestLevel = p.DisplayedAudioLevel;
+            }
+        }
+        foreach (var p in Participants)
+        {
+            var shouldHighlight = ReferenceEquals(p, loudest);
+            if (p.IsActiveSpeaker != shouldHighlight)
+                p.IsActiveSpeaker = shouldHighlight;
+        }
+
         // If sort mode is LoudestFirst, refresh the view so the new audio
         // peaks re-evaluate the sort. Skipped for the other sort modes
         // since their keys (name, online state) don't change every tick —
diff --git a/src/TeamsISO.App/ViewModels/ParticipantViewModel.cs b/src/TeamsISO.App/ViewModels/ParticipantViewModel.cs
index 21d0833..72d51c7 100644
--- a/src/TeamsISO.App/ViewModels/ParticipantViewModel.cs
+++ b/src/TeamsISO.App/ViewModels/ParticipantViewModel.cs
@@ -44,6 +44,19 @@ public sealed class ParticipantViewModel : ObservableObject
     /// <summary>True when <see cref="Thumbnail"/> is non-null. Bound to Visibility in XAML.</summary>
     public bool HasThumbnail => _thumbnail is not null;
 
+    /// <summary>
+    /// True when this participant is currently the loudest among the live
+    /// set — set by MainViewModel at the 1Hz stats tick. Bound to a cyan
+    /// border accent on the DataGrid row so operators can spot who's
+    /// speaking without watching every VU bar individually.
+    /// </summary>
+    public bool IsActiveSpeaker
+    {
+        get => _isActiveSpeaker;
+        internal set => SetField(ref _isActiveSpeaker, value);
+    }
+    private bool _isActiveSpeaker;
+
     public ParticipantViewModel(IIsoController controller, Participant participant, ToastViewModel? toast = null)
     {
         _controller = controller;