Born Eugene Reynolds Blumenthal in Cleveland, Ohio, he was raised in Detroit, where his father Frank was a businessman and entrepreneur. He made his screen debut in the 1934 Our Gang short Washee Ironee, and for the next three decades made numerous appearances in films such as In Old Chicago, Love Finds Andy Hardy, Boys Town, and the Country Girl and television series like I Love Lucy, Armstrong Circle Theatre, Whirlybirds, and Hallmark Hall of Fame.
In 1957, Reynolds joined forces with Frank Gruber and James Brooks to create Tales of Wells Fargo for NBC. During the program's five-year run he wrote and directed numerous episodes. Additional directing credits include multiple episodes of Leave It to Beaver, The Andy Griffith Show, The Farmer's Daughter, F Troop, Hogan's Heroes, Room 222, and Many Happy Returns.
As a writer, director, and producer, Reynolds was involved with two highly successful CBS series in the 1970s and early 1980s. Between 1972 and 1983, he produced 121 episodes of M*A*S*H, for which he wrote eleven episodes and directed twenty-four. During that same period, he produced twenty episodes of Lou Grant, for which he wrote 111 episodes and directed eleven.
Reynolds has been nominated for twenty-four Emmy Awards and won six times, including Outstanding Comedy Series for M*A*S*H and Outstanding Drama Series twice for Lou Grant, which also earned him a Humanitas Prize. He won the Directors Guild of America Award for Outstanding Direction of a Comedy Series twice for M*A*S*H and the Directors Guild of America Award for Outstanding Direction of a Drama Series once for Lou Grant.
Reynolds was elected President of the Directors Guild of America in 1993, a post he held for four years.
Reynolds was married to actress Bonnie Jones from 1967 until 1976, when the couple divorced. He and his current wife Ann married in 1979 and have one son, Andrew.