Ernest was a son of John II and ruled the duchy of Bavaria-Munich together with his brother William III.

He restrained uprisings of the citizenry of Munich in 1396 and 1410 and forced his uncle Stephen III to confine his reign to Bavaria-Ingolstadt in 1402.

Afterwards Ernest still fought several times successfully against the dukes of Bavaria-Ingolstadt Stephen III and his son Louis VII the Bearded as ally of Henry XVI of Bavaria-Landshut.

As ally of the House of Luxembourg Ernest backed his deposed brother in law Wenceslaus against the new king Rupert of the older branch of his own Wittelsbach dynasty as well as Wenceslaus' brother Sigismund in his wars against the supporters of Jan Hus.

When his son Albert III married secretly the maid Agnes Bernauer in 1432, Ernest ordered her murdered.