diff --git a/browser/ui/views/side_panel/brave_read_later_side_panel_view.cc b/browser/ui/views/side_panel/brave_read_later_side_panel_view.cc
index 39123865c386..25841064d29b 100644
--- a/browser/ui/views/side_panel/brave_read_later_side_panel_view.cc
+++ b/browser/ui/views/side_panel/brave_read_later_side_panel_view.cc
@@ -11,6 +11,8 @@
 #include "brave/grit/brave_generated_resources.h"
 #include "brave/grit/brave_theme_resources.h"
 #include "chrome/browser/ui/views/side_panel/read_later_side_panel_web_view.h"
+#include "chrome/browser/ui/views/side_panel/side_panel_content_proxy.h"
+#include "chrome/browser/ui/views/side_panel/side_panel_util.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/font_list.h"
@@ -78,11 +80,36 @@ BraveReadLaterSidePanelView::BraveReadLaterSidePanelView(
   AddChildView(std::make_unique<ReadLaterSidePanelHeaderView>());
   AddChildView(std::make_unique<views::Separator>())
       ->SetColorId(kColorSidebarPanelHeaderSeparator);
-  AddChildView(std::make_unique<ReadLaterSidePanelWebView>(browser, close_cb))
-      ->SetProperty(
-          views::kFlexBehaviorKey,
-          views::FlexSpecification(views::MinimumFlexSizeRule::kPreferred,
-                                   views::MaximumFlexSizeRule::kUnbounded));
+  auto* web_view = AddChildView(
+      std::make_unique<ReadLaterSidePanelWebView>(browser, close_cb));
+  web_view->SetProperty(
+      views::kFlexBehaviorKey,
+      views::FlexSpecification(views::MinimumFlexSizeRule::kPreferred,
+                               views::MaximumFlexSizeRule::kUnbounded));
+
+  // Originally SidePanelEntry's Content was ReadLaterSidePanelWebView
+  // and it's availability is set to true when SidePanelWebUIView::ShowUI()
+  // and then proxy's availability callback is executed.
+  // However, we use parent view(BraveReadLaterSidePanelView) to have
+  // panel specific header view and this class becomes SidePanelEntry's Content.
+  // To make this content available when SidePanelWebUIVew::ShowUI() is called,
+  // this observes WebView's visibility because it's set as visible when
+  // ShowUI() is called.
+  // NOTE: If we use our own reading list page and it has loading spinner, maybe
+  // we can set `true` here.
+  SidePanelUtil::GetSidePanelContentProxy(this)->SetAvailable(false);
+  observation_.Observe(web_view);
+}
+
+void BraveReadLaterSidePanelView::OnViewVisibilityChanged(
+    views::View* observed_view,
+    views::View* starting_view) {
+  // Once it becomes available, stop observing becuase its availablity is
+  // not changed from now on.
+  if (observed_view->GetVisible()) {
+    SidePanelUtil::GetSidePanelContentProxy(this)->SetAvailable(true);
+    observation_.Reset();
+  }
 }
 
 BraveReadLaterSidePanelView::~BraveReadLaterSidePanelView() = default;
diff --git a/browser/ui/views/side_panel/brave_read_later_side_panel_view.h b/browser/ui/views/side_panel/brave_read_later_side_panel_view.h
index 21c758bf21fa..d68e1489fb41 100644
--- a/browser/ui/views/side_panel/brave_read_later_side_panel_view.h
+++ b/browser/ui/views/side_panel/brave_read_later_side_panel_view.h
@@ -7,12 +7,15 @@
 #define BRAVE_BROWSER_UI_VIEWS_SIDE_PANEL_BRAVE_READ_LATER_SIDE_PANEL_VIEW_H_
 
 #include "base/functional/callback_forward.h"
+#include "base/scoped_observation.h"
 #include "ui/views/view.h"
+#include "ui/views/view_observer.h"
 
 class Browser;
 
 // Gives reading list specific header view with web view.
-class BraveReadLaterSidePanelView : public views::View {
+class BraveReadLaterSidePanelView : public views::View,
+                                    public views::ViewObserver {
  public:
   BraveReadLaterSidePanelView(Browser* browser,
                               base::RepeatingClosure close_cb);
@@ -20,6 +23,12 @@ class BraveReadLaterSidePanelView : public views::View {
   BraveReadLaterSidePanelView(const BraveReadLaterSidePanelView&) = delete;
   BraveReadLaterSidePanelView& operator=(const BraveReadLaterSidePanelView&) =
       delete;
+
+ private:
+  void OnViewVisibilityChanged(views::View* observed_view,
+                               views::View* starting_view) override;
+
+  base::ScopedObservation<views::View, views::ViewObserver> observation_{this};
 };
 
 #endif  // BRAVE_BROWSER_UI_VIEWS_SIDE_PANEL_BRAVE_READ_LATER_SIDE_PANEL_VIEW_H_