Hayes played college basketball at the University of Houston, where he was named twice to the NCAA All-American First Team and was named both the Sporting News and AP Player of the Year in 1968. He was drafted as the first overall pick in the 1968 draft by the Rockets.

In his 16 year career, he played for the Rockets and Bullets. He was named a NBA All Star 12 times, was the NBA scoring champion in 1969, and helped lead the 1978 Bullets to an NBA Championship. 

His number 11 was retired by the bullets and in 1990 he was inducted into the Naismith Memorial Basketball Hall of Fame.