The Crown of Ireland Act 1542 is an Act that was passed by the Parliament of Ireland on 18 June 1542, which created the title of "King of Ireland" for monarchs of England and their successors; previous monarchs had ruled Ireland as Lords of Ireland. The first monarch to hold the title was King Henry VIII of England.

The Kingdom of Ireland was a monarchy on the island of Ireland that was a client state of England and then of Great Britain. It existed from 1542 to the end of 1800. It was ruled by the monarchs of England and then of Great Britain, and was administered from Dublin Castle by a viceroy appointed by the English king: the Lord Deputy of Ireland. Aside from brief periods, the state was dominated by the Protestant English minority. The Protestant Church of Ireland was the state church. The Parliament of Ireland was composed of Anglo-Irish nobles. From 1661, the administration controlled an Irish army. Although styled a kingdom, for most of its history it was, de facto, an English dependency. This status was enshrined in Poynings' Law and in the Declaratory Act of 1719.