Joachim Ernst, Margrave of Brandenburg-Ansbach (22 June 1583 in Cölln an der Spree – 7 March 1625 in Ansbach) was a German nobleman.

[1] He took over in 1603, the government of the Margraviate of Brandenburg-Ansbach, after the old line of Franconian Hohenzollerns died out with the death of George Fredrick the Elder of the Ansbach-Jägerndorf branch.

His predecessor, George Frederick had settled the succession of his two Franconian possessions (Brandenburg-Ansbach and Brandenburg-Kulmbach) in the House Treaty of Gera of 1598.

In the religious conflicts of the early 17th Century, Joachim Ernst tended to be in the Protestant-Calvinist camp and he also supported the Dutch struggle for independence.

After the dissolution of the Union, Joachim Ernst was held responsible for the outbreak of war by his Catholic opponents and he then completely distanced himself from his former allies.