He made his acting debut in 1940 on The Bishop and the Gargoyle radio series. He played the Gargoyle, replacing Milton Herman, who had previously portrayed the character. From 1942 to 1946, he provided the voice of "Tank", the mechanic, who aides the title character in Hop Harrigan. In 1950, he starred in One Thousand Dollars Reward, a rare crime drama, where after the crime play had ended, the host would place a telephone call to a random listener, who would then try to solve the mystery. Lynch also appeared on the radio shows The Falcon, 21st Precinct, and Gunsmoke. Later, in 1952, he played both Christopher Gard and Steve Lacey in Cafe Istanbul on CBS radio.

From 1949 to 1954, Lynch starred in The Plainclothesman on the DuMont Television Network. He appeared in numerous television series. He made three guest appearances on Perry Mason, including the role of Wallace Lang in "The Case of the Stuttering Bishop" in 1959, and Robert Hayden in "The Case of the Irate Inventor" in 1960. Some of the other series in which Lynch appeared are Peter Gunn, Zorro, Have Gun - Will Travel ("Love of a bad woman"), Checkmate ("Cyanide Touch"), The Asphalt Jungle, The Honeymooners, The Fugitive, The Andy Griffith Show, The Dick Van Dyke Show, Blue Light, Adam-12, Star Trek ("The Devil in the Dark"), Maverick, All In The Family, The Twilight Zone ("Mr. Denton on Doomsday"), The Rifleman, and The Wild Wild West. Between 1972 and 1977, he made 16 guest appearances on McCloud, performing as a police sergeant and later a detective named Grover on the series. He previously appeared in 12 episodes of Gunsmoke, 10 episodes of The F.B.I., nine episodes of Bonanza, and six episodes in both The Virginian and Gomer Pyle, USMC. Among the feature films in which he appeared are I Married a Monster from Outer Space, North By North West, The Lawbreakers, Pork Chop Hill, Anatomy of a Murder and Tora! Tora! Tora!. Lynch's last credited performance was in the role of Rear Admiral Talbot Gray in the 1983 seven-part miniseries The Winds of War.

Even though Lynch still had a very successful career as an actor by the 1970s, he began looking for another, more steady source of income. He explained in a 1975 newspaper interview: "In acting you just can't predict the jobs that will come along. If you could, you could budget." With such income uncertainty in mind as he grew older, Lynch bought a flower shop in North Hollywood a "few years" before the noted interview. He began studying floriculture, taking courses in the art of floral arranging and design, and then providing flowers for local weddings, receptions, and other events. According to Lynch, his many years of experience performing on decorated sets for movies and television series proved to be a benefit to him in his new Business. "Actually," he observed, "servicing a wedding is like ordering flowers for a studio set".

Lynch died at age 79 from a virus on February 13, 1990, in Burbank, California. He was buried at the San Fernando Mission Cemetery in Mission Hills, Los Angeles.