diff --git a/osu.Game/Online/Multiplayer/Countdown/CountdownChangedEvent.cs b/osu.Game/Online/Multiplayer/Countdown/CountdownChangedEvent.cs
new file mode 100644
index 0000000000..b067f3b235
--- /dev/null
+++ b/osu.Game/Online/Multiplayer/Countdown/CountdownChangedEvent.cs
@@ -0,0 +1,22 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+#nullable enable
+
+using MessagePack;
+
+namespace osu.Game.Online.Multiplayer.Countdown
+{
+    /// <summary>
+    /// Indicates a change to the <see cref="MultiplayerRoom"/>'s countdown.
+    /// </summary>
+    [MessagePackObject]
+    public class CountdownChangedEvent : MatchServerEvent
+    {
+        /// <summary>
+        /// The new countdown.
+        /// </summary>
+        [Key(0)]
+        public MultiplayerCountdown? Countdown { get; set; }
+    }
+}
diff --git a/osu.Game/Online/Multiplayer/Countdown/MatchStartCountdownRequest.cs b/osu.Game/Online/Multiplayer/Countdown/MatchStartCountdownRequest.cs
new file mode 100644
index 0000000000..04e7f506c2
--- /dev/null
+++ b/osu.Game/Online/Multiplayer/Countdown/MatchStartCountdownRequest.cs
@@ -0,0 +1,23 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using MessagePack;
+
+#nullable enable
+
+namespace osu.Game.Online.Multiplayer.Countdown
+{
+    /// <summary>
+    /// A request for a countdown to start the match.
+    /// </summary>
+    [MessagePackObject]
+    public class MatchStartCountdownRequest : MatchUserRequest
+    {
+        /// <summary>
+        /// How long the countdown should last.
+        /// </summary>
+        [Key(0)]
+        public TimeSpan Delay { get; set; }
+    }
+}
diff --git a/osu.Game/Online/Multiplayer/Countdown/StopCountdownRequest.cs b/osu.Game/Online/Multiplayer/Countdown/StopCountdownRequest.cs
new file mode 100644
index 0000000000..20a0e32734
--- /dev/null
+++ b/osu.Game/Online/Multiplayer/Countdown/StopCountdownRequest.cs
@@ -0,0 +1,17 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+#nullable enable
+
+using MessagePack;
+
+namespace osu.Game.Online.Multiplayer.Countdown
+{
+    /// <summary>
+    /// Request to stop the current countdown.
+    /// </summary>
+    [MessagePackObject]
+    public class StopCountdownRequest : MatchUserRequest
+    {
+    }
+}
diff --git a/osu.Game/Online/Multiplayer/MatchServerEvent.cs b/osu.Game/Online/Multiplayer/MatchServerEvent.cs
index 891fb2cc3b..4ce55e424d 100644
--- a/osu.Game/Online/Multiplayer/MatchServerEvent.cs
+++ b/osu.Game/Online/Multiplayer/MatchServerEvent.cs
@@ -1,8 +1,11 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+#nullable enable
+
 using System;
 using MessagePack;
+using osu.Game.Online.Multiplayer.Countdown;
 
 namespace osu.Game.Online.Multiplayer
 {
@@ -11,6 +14,8 @@ namespace osu.Game.Online.Multiplayer
     /// </summary>
     [Serializable]
     [MessagePackObject]
+    // IMPORTANT: Add rules to SignalRUnionWorkaroundResolver for new derived types.
+    [Union(0, typeof(CountdownChangedEvent))]
     public abstract class MatchServerEvent
     {
     }
diff --git a/osu.Game/Online/Multiplayer/MatchStartCountdown.cs b/osu.Game/Online/Multiplayer/MatchStartCountdown.cs
new file mode 100644
index 0000000000..6c1cdd97d3
--- /dev/null
+++ b/osu.Game/Online/Multiplayer/MatchStartCountdown.cs
@@ -0,0 +1,17 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+#nullable enable
+
+using MessagePack;
+
+namespace osu.Game.Online.Multiplayer
+{
+    /// <summary>
+    /// A <see cref="MultiplayerCountdown"/> which will start the match after ending.
+    /// </summary>
+    [MessagePackObject]
+    public class MatchStartCountdown : MultiplayerCountdown
+    {
+    }
+}
diff --git a/osu.Game/Online/Multiplayer/MatchTypes/TeamVersus/ChangeTeamRequest.cs b/osu.Game/Online/Multiplayer/MatchTypes/TeamVersus/ChangeTeamRequest.cs
index 9c3b07049c..a26a2b3fc2 100644
--- a/osu.Game/Online/Multiplayer/MatchTypes/TeamVersus/ChangeTeamRequest.cs
+++ b/osu.Game/Online/Multiplayer/MatchTypes/TeamVersus/ChangeTeamRequest.cs
@@ -7,6 +7,7 @@ using MessagePack;
 
 namespace osu.Game.Online.Multiplayer.MatchTypes.TeamVersus
 {
+    [MessagePackObject]
     public class ChangeTeamRequest : MatchUserRequest
     {
         [Key(0)]
diff --git a/osu.Game/Online/Multiplayer/MatchUserRequest.cs b/osu.Game/Online/Multiplayer/MatchUserRequest.cs
index 8c6809e7f3..fa7bdd8afe 100644
--- a/osu.Game/Online/Multiplayer/MatchUserRequest.cs
+++ b/osu.Game/Online/Multiplayer/MatchUserRequest.cs
@@ -3,6 +3,7 @@
 
 using System;
 using MessagePack;
+using osu.Game.Online.Multiplayer.Countdown;
 using osu.Game.Online.Multiplayer.MatchTypes.TeamVersus;
 
 namespace osu.Game.Online.Multiplayer
@@ -12,7 +13,10 @@ namespace osu.Game.Online.Multiplayer
     /// </summary>
     [Serializable]
     [MessagePackObject]
-    [Union(0, typeof(ChangeTeamRequest))] // IMPORTANT: Add rules to SignalRUnionWorkaroundResolver for new derived types.
+    // IMPORTANT: Add rules to SignalRUnionWorkaroundResolver for new derived types.
+    [Union(0, typeof(ChangeTeamRequest))]
+    [Union(1, typeof(MatchStartCountdownRequest))]
+    [Union(2, typeof(StopCountdownRequest))]
     public abstract class MatchUserRequest
     {
     }
diff --git a/osu.Game/Online/Multiplayer/MultiplayerCountdown.cs b/osu.Game/Online/Multiplayer/MultiplayerCountdown.cs
new file mode 100644
index 0000000000..63bb47b295
--- /dev/null
+++ b/osu.Game/Online/Multiplayer/MultiplayerCountdown.cs
@@ -0,0 +1,24 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+#nullable enable
+
+using System;
+using MessagePack;
+
+namespace osu.Game.Online.Multiplayer
+{
+    /// <summary>
+    /// Describes the current countdown in a <see cref="MultiplayerRoom"/>.
+    /// </summary>
+    [MessagePackObject]
+    [Union(0, typeof(MatchStartCountdown))] // IMPORTANT: Add rules to SignalRUnionWorkaroundResolver for new derived types.
+    public abstract class MultiplayerCountdown
+    {
+        /// <summary>
+        /// The time at which the countdown will end.
+        /// </summary>
+        [Key(0)]
+        public DateTimeOffset EndTime { get; set; }
+    }
+}
diff --git a/osu.Game/Online/Multiplayer/MultiplayerRoom.cs b/osu.Game/Online/Multiplayer/MultiplayerRoom.cs
index a60e70dab3..e215498ff9 100644
--- a/osu.Game/Online/Multiplayer/MultiplayerRoom.cs
+++ b/osu.Game/Online/Multiplayer/MultiplayerRoom.cs
@@ -54,6 +54,12 @@ namespace osu.Game.Online.Multiplayer
         [Key(6)]
         public IList<MultiplayerPlaylistItem> Playlist { get; set; } = new List<MultiplayerPlaylistItem>();
 
+        /// <summary>
+        /// The currently-running countdown.
+        /// </summary>
+        [Key(7)]
+        public MultiplayerCountdown? Countdown { get; set; }
+
         [JsonConstructor]
         [SerializationConstructor]
         public MultiplayerRoom(long roomId)
diff --git a/osu.Game/Online/SignalRWorkaroundTypes.cs b/osu.Game/Online/SignalRWorkaroundTypes.cs
index f69d23d81c..3e2b697337 100644
--- a/osu.Game/Online/SignalRWorkaroundTypes.cs
+++ b/osu.Game/Online/SignalRWorkaroundTypes.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using osu.Game.Online.Multiplayer;
+using osu.Game.Online.Multiplayer.Countdown;
 using osu.Game.Online.Multiplayer.MatchTypes.TeamVersus;
 
 namespace osu.Game.Online
@@ -18,8 +19,12 @@ namespace osu.Game.Online
         internal static readonly IReadOnlyList<(Type derivedType, Type baseType)> BASE_TYPE_MAPPING = new[]
         {
             (typeof(ChangeTeamRequest), typeof(MatchUserRequest)),
+            (typeof(MatchStartCountdownRequest), typeof(MatchUserRequest)),
+            (typeof(StopCountdownRequest), typeof(MatchUserRequest)),
+            (typeof(CountdownChangedEvent), typeof(MatchServerEvent)),
             (typeof(TeamVersusRoomState), typeof(MatchRoomState)),
             (typeof(TeamVersusUserState), typeof(MatchUserState)),
+            (typeof(MatchStartCountdown), typeof(MultiplayerCountdown))
         };
     }
 }