The 60-year veteran of the small screen passed away Saturday in Thousand Oaks, Calif., while surrounded by family, the Hollywood Reporter said.
Although "S.W.A.T." lasted just two seasons, and Forrest would go on to appear in dozens of shows and movies, audiences loved him best for his turn as team leader Harrelson. The actor would tip his hat to the popularity of the show nearly 40 years after it went off the air, making a small cameo in the 2003 film based on the series.
Forrest began his career in theater at UCLA, where he graduated with honors in 1950 and went on to work in the La Jolla Playhouse in Southern California. There he was discovered by Gregory Peck, who spotted him in a summer stock production and arranged for his screen test with MGM.
He won a Golden Globe for New Star of the Year for his role in the 1953 film "So Big."
Forrest was born William Forrest Andrews in 1925 in Huntsville, Texas, and is survived by his wife Christine, whom he married in 1948, and their three sons, Michael, Forrest and Stephen Andrews.