--- a/devtools/client/webconsole/store.js
+++ b/devtools/client/webconsole/store.js
@@ -70,17 +70,18 @@ function configureStore(hud, options = {
 
   return createStore(
     createRootReducer(),
     initialState,
     compose(
       applyMiddleware(thunk.bind(null, {prefsService})),
       enableActorReleaser(hud),
       enableBatching(),
-      enableNetProvider(hud)
+      enableNetProvider(hud),
+      enableMessagesCacheClearing(hud),
     )
   );
 }
 
 function thunk(options = {}, { dispatch, getState }) {
   return next => action => {
     return (typeof action === "function")
       ? action(dispatch, getState, options)
@@ -247,16 +248,39 @@ function enableNetProvider(hud) {
       }
 
       return newState;
     }
 
     return next(netProviderEnhancer, initialState, enhancer);
   };
 }
+
+/**
+ * This enhancer is responsible for clearing the messages caches using the
+ * webconsoleClient when the user clear the messages (either by direct UI action, or via
+ * `console.clear()`).
+ */
+function enableMessagesCacheClearing(hud) {
+  return next => (reducer, initialState, enhancer) => {
+    function messagesCacheClearingEnhancer(state, action) {
+      state = reducer(state, action);
+
+      let webConsoleClient = hud && hud.proxy ? hud.proxy.webConsoleClient : null;
+      if (webConsoleClient && action.type === MESSAGES_CLEAR) {
+        webConsoleClient.clearNetworkRequests();
+        webConsoleClient.clearMessagesCache();
+      }
+      return state;
+    }
+
+    return next(messagesCacheClearingEnhancer, initialState, enhancer);
+  };
+}
+
 /**
  * Helper function for releasing backend actors.
  */
 function releaseActors(removedActors, proxy) {
   if (!proxy) {
     return;
   }
 

--- a/devtools/client/webconsole/test/mochitest/browser.ini
+++ b/devtools/client/webconsole/test/mochitest/browser.ini
@@ -161,16 +161,17 @@ support-files =
   testscript.js
   !/devtools/client/netmonitor/test/sjs_cors-test-server.sjs
   !/image/test/mochitest/blue.png
   !/devtools/client/shared/test/shared-head.js
   !/devtools/client/shared/test/test-actor.js
   !/devtools/client/shared/test/test-actor-registry.js
 
 [browser_console.js]
+[browser_console_clear_cache.js]
 [browser_console_clear_method.js]
 skip-if = true # Bug 1437843
 [browser_console_consolejsm_output.js]
 [browser_console_context_menu_entries.js]
 skip-if = (os == "linux" && (debug || ccov)) # Bug 1440059
 [browser_console_dead_objects.js]
 [browser_console_devtools_loader_exception.js]
 [browser_console_error_source_click.js]
@@ -233,16 +234,17 @@ subsuite = clipboard
 [browser_webconsole_allow_mixedcontent_securityerrors.js]
 tags = mcb
 [browser_webconsole_batching.js]
 [browser_webconsole_block_mixedcontent_securityerrors.js]
 tags = mcb
 [browser_webconsole_cached_messages.js]
 [browser_webconsole_cd_iframe.js]
 [browser_webconsole_certificate_messages.js]
+[browser_webconsole_clear_cache.js]
 [browser_webconsole_click_function_to_source.js]
 [browser_webconsole_clickable_urls.js]
 [browser_webconsole_close_unfocused_window.js]
 [browser_webconsole_closing_after_completion.js]
 [browser_webconsole_close_sidebar.js]
 [browser_webconsole_closure_inspection.js]
 skip-if = true # Bug 1405250
 [browser_webconsole_console_api_iframe.js]

new file mode 100644
--- /dev/null
+++ b/devtools/client/webconsole/test/mochitest/browser_console_clear_cache.js
@@ -0,0 +1,39 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// Check that clearing the browser console output also clears the console cache.
+
+"use strict";
+
+const TEST_URI = "data:text/html;charset=utf8,Test browser console clear cache";
+
+add_task(async function() {
+  await addTab(TEST_URI);
+  let hud = await HUDService.toggleBrowserConsole();
+  const CACHED_MESSAGE = "CACHED_MESSAGE";
+  await logTextToConsole(hud, CACHED_MESSAGE);
+
+  info("Click the clear output button");
+  const onBrowserConsoleOutputCleared = waitFor(
+    () => !findMessage(hud, CACHED_MESSAGE)
+  );
+  hud.ui.window.document.querySelector(".devtools-clear-icon").click();
+  await onBrowserConsoleOutputCleared;
+
+  info("Close and re-open the browser console");
+  await HUDService.toggleBrowserConsole();
+  hud = await HUDService.toggleBrowserConsole();
+
+  info("Log a smoke message in order to know that the console is ready");
+  await logTextToConsole(hud, "Smoke message");
+  is(findMessage(hud, CACHED_MESSAGE), null, "The cached message is not visible anymore");
+});
+
+function logTextToConsole(hud, text) {
+  const onMessage = waitForMessage(hud, text);
+  ContentTask.spawn(gBrowser.selectedBrowser, text, function(str) {
+    content.wrappedJSObject.console.log(str);
+  });
+  return onMessage;
+}

new file mode 100644
--- /dev/null
+++ b/devtools/client/webconsole/test/mochitest/browser_webconsole_clear_cache.js
@@ -0,0 +1,64 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// Check that clearing the output also clears the console cache.
+
+"use strict";
+
+const TEST_URI = "data:text/html;charset=utf8,Test clear cache";
+
+add_task(async function() {
+  const tab = await addTab(TEST_URI);
+  let hud = await openConsole(tab);
+
+  const CACHED_MESSAGE = "CACHED_MESSAGE";
+  await logTextToConsole(hud, CACHED_MESSAGE);
+
+  info("Close and re-open the console");
+  await closeToolbox();
+  hud = await openConsole(tab);
+
+  await waitFor(() => findMessage(hud, CACHED_MESSAGE));
+
+  info("Click the clear output button");
+  let onOutputCleared = waitFor(() => !findMessage(hud, CACHED_MESSAGE));
+  hud.ui.window.document.querySelector(".devtools-clear-icon").click();
+  await onOutputCleared;
+
+  info("Close and re-open the console");
+  await closeToolbox();
+  hud = await openConsole(tab);
+
+  info("Log a smoke message in order to know that the console is ready");
+  await logTextToConsole(hud, "Smoke message");
+  is(findMessage(hud, CACHED_MESSAGE), null, "The cached message is not visible anymore");
+
+  // Test that we also clear the cache when calling console.clear().
+  const NEW_CACHED_MESSAGE = "NEW_CACHED_MESSAGE";
+  await logTextToConsole(hud, NEW_CACHED_MESSAGE);
+
+  info("Send a console.clear() from the content page");
+  const onConsoleCleared = waitForMessage(hud, "Console was cleared");
+  ContentTask.spawn(gBrowser.selectedBrowser, {}, () => {
+    content.wrappedJSObject.console.clear();
+  });
+  await onConsoleCleared;
+
+  info("Close and re-open the console");
+  await closeToolbox();
+  hud = await openConsole(tab);
+
+  info("Log a smoke message in order to know that the console is ready");
+  await logTextToConsole(hud, "Second smoke message");
+  is(findMessage(hud, NEW_CACHED_MESSAGE), null,
+    "The new cached message is not visible anymore");
+});
+
+function logTextToConsole(hud, text) {
+  const onMessage = waitForMessage(hud, text);
+  ContentTask.spawn(gBrowser.selectedBrowser, text, function(str) {
+    content.wrappedJSObject.console.log(str);
+  });
+  return onMessage;
+}