Neither musician has worked on the Oscars before, but they'll be the music consultants for the awards show, which will be held Feb. 26, 2012.
Zimmer, 54, is an Oscar-winning composer who took home an award for the original score for 1994's "The Lion King." He also earned multiple nominations for scoring films such as "Inception" and "Gladiator."
Williams, 38, is a Grammy-winning rapper and producer who has worked with artists such as Jay-Z, Justin Timberlake and Beyonce.
The Associated Press contributed to this report.