diff --git a/src/knotification.h b/src/knotification.h
--- a/src/knotification.h
+++ b/src/knotification.h
@@ -398,8 +398,33 @@
     void setPixmap(const QPixmap &pix);
 
     /**
+     * @return the default action, or an empty string if not set
+     */
+    QString defaultAction() const;
+
+    /**
+     * Set a default action that will be triggered when the notification is
+     * activated (typically, by clicking on the notification popup). The default
+     * action should raise a window belonging to the application that sent it.
+     *
+     * The string will be used as a label for the action, so ideally it should
+     * be wrapped in i18n() or tr() calls.
+     *
+     * The visual representation of actions depends on the notification server.
+     * In Plasma and Gnome desktops, the actions are performed by clicking on
+     * the notification popup, and the label is not presented to the user.
+     *
+     *
+     * @param action Label of the default action. The label might or might not
+     * be displayed to the user by the notification server, depending on the
+     * implementation. Passing an empty string disables the default action.
+     */
+    void setDefaultAction(const QString &defaultAction);
+
+    /**
      * @return the list of actions
      */
+    //KF6: Rename to "additionalActions"?
     QStringList actions() const;
 
     /**
@@ -414,6 +439,7 @@
      *
      * @param actions List of strings used as action labels
      */
+    //KF6: Rename to "setAdditionalActions"?
     void setActions(const QStringList &actions);
 
     /**
diff --git a/src/knotification.cpp b/src/knotification.cpp
--- a/src/knotification.cpp
+++ b/src/knotification.cpp
@@ -52,6 +52,7 @@
     QString title;
     QString text;
     QString iconName;
+    QString defaultAction;
     QStringList actions;
     QPixmap pixmap;
     ContextList contexts;
@@ -210,6 +211,24 @@
     }
 }
 
+void KNotification::setDefaultAction(const QString &defaultAction)
+{
+    if (defaultAction == d->defaultAction) {
+        return;
+    }
+
+    d->needUpdate = true;
+    d->defaultAction = defaultAction;
+    if (d->id >= 0) {
+        d->updateTimer.start();
+    }
+}
+
+QString KNotification::defaultAction() const
+{
+    return d->defaultAction;
+}
+
 KNotification::ContextList KNotification::contexts() const
 {
     return d->contexts;
diff --git a/src/notifybypopup.cpp b/src/notifybypopup.cpp
--- a/src/notifybypopup.cpp
+++ b/src/notifybypopup.cpp
@@ -477,7 +477,11 @@
 
     KNotification *n = *iter;
     if (n) {
-        emit actionInvoked(n->id(), actionKey.toUInt());
+        if (actionKey == QStringLiteral("default")) {
+            emit actionInvoked(n->id(), 0);
+        } else {
+            emit actionInvoked(n->id(), actionKey.toUInt());
+        }
     } else {
         d->galagoNotifications.erase(iter);
     }
@@ -667,6 +671,11 @@
     // (i.e. starting from 1)
     QStringList actionList;
     if (popupServerCapabilities.contains(QStringLiteral("actions"))) {
+        QString defaultAction = notification->defaultAction();
+        if (!defaultAction.isEmpty()) {
+            actionList.append(QStringLiteral("default"));
+            actionList.append(defaultAction);
+        }
         int actId = 0;
         Q_FOREACH (const QString &actionName, notification->actions()) {
             actId++;