diff --git a/HellionChat/PluginHostFactory.cs b/HellionChat/PluginHostFactory.cs
index ed5f2fa..c609506 100644
--- a/HellionChat/PluginHostFactory.cs
+++ b/HellionChat/PluginHostFactory.cs
@@ -145,6 +145,13 @@ internal static class PluginHostFactory
             sp.GetRequiredService<ThemeRegistry>(),
             sp.GetRequiredService<FontManager>()
         ));
+        services.AddSingleton(sp => new Ui.Windows.MainWindow(
+            sp.GetRequiredService<Ui.Components.HonorificHeader>(),
+            sp.GetRequiredService<Ui.Components.Sidebar>(),
+            sp.GetRequiredService<Ui.Components.MessageList>(),
+            sp.GetRequiredService<Ui.Components.InputBar>(),
+            sp.GetRequiredService<Ui.Components.StatusBar>()
+        ));
         services.AddSingleton(sp => new Integrations.FailedTellNotifier(
             sp.GetRequiredService<ILogger<Integrations.FailedTellNotifier>>()
         ));
diff --git a/HellionChat/Ui/Components/InputBar.cs b/HellionChat/Ui/Components/InputBar.cs
index be37f9c..a10cca3 100644
--- a/HellionChat/Ui/Components/InputBar.cs
+++ b/HellionChat/Ui/Components/InputBar.cs
@@ -16,7 +16,7 @@ namespace HellionChat.Ui.Components;
 // picker overlay.
 internal sealed class InputBar
 {
-    private const float Height = 32f;
+    public const float Height = 32f;
     private const float PillHeight = 22f;
     private const float PillPaddingX = 8f;
     private const int BufferCapacity = 500;
diff --git a/HellionChat/Ui/Windows/MainWindow.cs b/HellionChat/Ui/Windows/MainWindow.cs
new file mode 100644
index 0000000..33b6b19
--- /dev/null
+++ b/HellionChat/Ui/Windows/MainWindow.cs
@@ -0,0 +1,121 @@
+using System.Numerics;
+using Dalamud.Bindings.ImGui;
+using Dalamud.Interface.Utility.Raii;
+using Dalamud.Interface.Windowing;
+
+namespace HellionChat.Ui.Windows;
+
+// Top-level chat window assembled from the components layer. Layout from
+// top to bottom: honorific header, horizontal body with sidebar + main
+// area (messages + input bar), and the status strip pinned to the
+// bottom. The window-level theme push stays on the global plugin draw
+// path for now — this window only composes content.
+//
+// Components are fully qualified through the Ui.Components prefix so the
+// old Ui.StatusBar type (still alive until the cleanup block removes it)
+// cannot shadow the new layer through parent-namespace resolution.
+internal sealed class MainWindow : Window
+{
+    private const float DefaultWidth = 620f;
+    private const float DefaultHeight = 340f;
+    private const float MinWidth = 480f;
+    private const float MinHeight = 260f;
+
+    private readonly Components.HonorificHeader _honorific;
+    private readonly Components.Sidebar _sidebar;
+    private readonly Components.MessageList _messages;
+    private readonly Components.InputBar _input;
+    private readonly Components.StatusBar _status;
+
+    private Tab? _activeTab;
+
+    public MainWindow(
+        Components.HonorificHeader honorific,
+        Components.Sidebar sidebar,
+        Components.MessageList messages,
+        Components.InputBar input,
+        Components.StatusBar status
+    )
+        : base($"{Plugin.PluginName}###hellion-main")
+    {
+        _honorific = honorific;
+        _sidebar = sidebar;
+        _messages = messages;
+        _input = input;
+        _status = status;
+
+        Size = new Vector2(DefaultWidth, DefaultHeight);
+        SizeCondition = ImGuiCond.FirstUseEver;
+        SizeConstraints = new WindowSizeConstraints
+        {
+            MinimumSize = new Vector2(MinWidth, MinHeight),
+            MaximumSize = new Vector2(float.MaxValue, float.MaxValue),
+        };
+        IsOpen = Plugin.Config.MainWindowOpen;
+        RespectCloseHotkey = false;
+    }
+
+    public Tab? ActiveTab => _activeTab;
+
+    // new-shadow on Window.Toggle so the open path also writes Config —
+    // OnClose already covers the close path through the base behaviour.
+    public new void Toggle()
+    {
+        IsOpen = !IsOpen;
+        Plugin.Config.MainWindowOpen = IsOpen;
+    }
+
+    public override void OnClose()
+    {
+        Plugin.Config.MainWindowOpen = false;
+    }
+
+    public override void Draw()
+    {
+        // First-frame seed: the active tab defaults to the first persisted
+        // tab so the message list isn't empty on a clean session.
+        if (_activeTab is null && Plugin.Config.Tabs.Count > 0)
+            _activeTab = Plugin.Config.Tabs[0];
+
+        var statusHeight = Components.StatusBar.Height;
+
+        using (var body = ImRaii.Child("##hellion-body", new Vector2(-1f, -statusHeight)))
+        {
+            if (body.Success)
+                DrawBody();
+        }
+
+        _status.Draw(_activeTab);
+    }
+
+    private void DrawBody()
+    {
+        var bodyWidth = ImGui.GetContentRegionAvail().X;
+        _honorific.Draw(bodyWidth);
+
+        using (ImRaii.Group())
+        {
+            _sidebar.Draw(bodyWidth, Plugin.Config.Tabs, ref _activeTab);
+        }
+
+        ImGui.SameLine();
+
+        using (ImRaii.Group())
+        {
+            DrawMainArea();
+        }
+    }
+
+    private void DrawMainArea()
+    {
+        var inputHeight = Components.InputBar.Height;
+
+        using (var messages = ImRaii.Child("##hellion-main-area", new Vector2(-1f, -inputHeight)))
+        {
+            if (messages.Success)
+                _messages.Draw(_activeTab!);
+        }
+
+        _input.Draw(_activeTab);
+    }
+}