Hillman was selected in the first round of the 1971 NBA draft (the 8th pick overall) by the Golden State Warriors, but opted instead to play for the Indiana Pacers of the American Basketball Association.

[2] Hillman played six seasons for the Pacers, who joined the National Basketball Association (NBA) with the ABA–NBA merger in June 1976.

[3][4] He would even be named the winner of the NBA's Slam Dunk Contest in the 1976–77 season, which was a precursor to the event that's known today, although he wouldn't be given an official trophy for it until March 8, 2017[5] In the final of that contest, which took place at halftime of Game 5 of the 1977 NBA Finals, Hillman defeated Larry McNeill of the Golden State Warriors.

Since he was not officially a member of any NBA team, instead of wearing a jersey, he competed in a plain white tank top.

Hillman also played for the United States men's national basketball team at the 1970 FIBA World Championship.