Catherine was the only daughter and second child of the Duke Henry I of Brunswick-Lüneburg († 1416) from his first marriage to Sophie († June 1400), daughter of Duke Wartislaw VI of Pomerania.

The elector lost a large part of his army in the Hussite Wars in 1421 in the Battle of Brüx.

During Frederick's absence, Electress Catherine organized another army of 20,000 men, which rushed to Frederick's aid, but was defeated devastatingly in the Battle of Aussig in 1426.

Catherine spent time with her husband, but more frequently alone, at Mildenstein Castle in Leisnig, which thereby developed into a private residence of the Saxon Electors.

She is buried in the Princely Chapel in Meissen Cathedral.