In 1972, Hayes was traded to the Baltimore Bullets, where he teamed with Hall-Of-Famer Wes Unseld to form a fierce and dominating frontcourt combination. The 18.1 rebounds per game Hayes averaged in 1974 is the third highest rebounding average of any NBA player since Wilt Chamberlain retired in 1973.
Hayes and Unseld later led the Washington Bullets to 3 NBA Finals (1975, 1978, and 1979), and an NBA title over The Seattle SuperSonics in 1978. He shined brightly, especially in the NBA playoffs. During the Bullets' championship season (1978), he averaged 21.8 points and 12.1 rebounds per game in 21 playoff games. One year later, he set an NBA Finals record for most offensive rebounds in a game (11), in a May 27, 1979 game against the SuperSonics.

This Baltimore Bullets jersey was signed in silver by Hayes and inscribed "HOF 90." This jersey includes a JSA sticker and COA.