Forrest was selected in the second round (19th pick overall) in the 1976 NBA draft by the Seattle SuperSonics. Forrest turned down the Sonics in favor of Athletes in Action and later signed with the Phoenix Suns in 1977.
Forrest served as a back-up for veteran center Alvan Adams in the 1978 and 1979 seasons. The Suns reached the Western Conference Finals in the 1979 NBA Playoffs, which saw Forrest play an expanded with an injured Adams unavailable for the first six games of the series. While in Phoenix, he averaged 15.3 minutes, 4.1 points, 4.2 rebounds and 2.2 assists per game. He retired on June 7, 1980.
Before Forrest was drafted by the Sonics, he was selected by the Phoenix Suns in the third round (54th overall) of the 1975 NBA draft and by the San Antonio Spurs in the 6th round (56th overall) of the 1975 ABA Draft. He chose to play the final season of his college career instead.
Personal
Forrest's nephew, Caleb (born 1986), played four years of college basketball at Washington State University.