In 1401, William was appointed Bishop of Paderborn by Pope Boniface IX through the influence of his uncle, Rupert, King of Germany.

Like his uncle, King Rupert, William was a follower of the Roman Popes.

Despite territorial policy successes, he faced opposition and renounced Paderborn in 1414.

He attempted to become Archbishop of Cologne but failed against Dietrich of Moers who also replaced William as Bishop of Paderborn.

William then married Dietrich's niece, Adelheid of Tecklenburg, and became the father of the new line of the Dukes of Jülich-Berg and Counts of Ravensberg, when his brother Adolf died without an heir.