He was born Frank Andrew Lovejoy, Jr., in the Bronx, New York, but grew up in New Jersey. His father, Frank Lovejoy, Sr., was a furniture salesman from Maine. His mother, Nora, was born in Massachusetts to Irish immigrant parents.
A successful radio actor, Lovejoy played Broadway Harry on the Gay Nineties Revue and was heard on the 1930s crime drama series Gang Busters. Lovejoy was a narrator (during the first season) for the show This Is Your FBI.
In radio soap operas, Lovejoy played Dr. Christopher Ellerbe in Valiant Lady, Sam Foster in This Day Is Ours, and he had the roles of Brad Forbes on Brave Tomorrow and Larry Halliday in Bright Horizon. He also played the title character on the syndicated The Blue Beetle in 1940, several episodes of The Whistler, and starred in the later newspaper drama series Night Beat in the early 1950s and in episodes of Suspense in the late 1950s. He also starred as John Malone in The Amazing Mr. Malone.
In films of the 1940s and 1950s, Lovejoy mostly played supporting roles. Appearing in movies such as Goodbye, My Fancy (1951) with Joan Crawford, and The Hitch-Hiker (1953) directed by Ida Lupino, Lovejoy was effective playing the movie's everyman in extraordinary situations. He was in several war movies, notably Stanley Kramer's Home of the Brave (1949), Breakthrough (1950), Joseph H. Lewis's Retreat, Hell! (1952) which portrayed the United States Marine Corps' retreat from the Chosin Reservoir (Changjin Reservoir) during the Korean War and as a Marine sergeant again in Beachhead (1954). In 1951, he had the title role in I Was a Communist for the FBI with co-stars Ron Hagerthy, Paul Picerni, and Philip Carey.
Lovejoy starred in two short-run TV series, Man Against Crime and Meet McGraw. Episodes of these two series have never been released commercially on DVD or VHS and never aired as reruns. Meet McGraw episodes were screened at the Mid-Atlantic Nostalgia Convention.
Lovejoy's final television performances include the episode "County General" (March 18, 1962) on the ABC series Bus Stop with Marilyn Maxwell in the role of Grace Sherwood. That same season, he appeared on the ABC crime drama Target: The Corruptors! about the efforts of a New York City reporter to expose organized crime.
Lovejoy was first married to Frances Williams (1901–59), but divorced in the late 1930s. In 1940, Lovejoy married actress Joan Banks (1918–1998), with whom he had a son and a daughter.
On October 2, 1962, Frank Lovejoy died of a heart attack in his sleep at his residence in New York City. His wife, Joan Banks, called for medical help after she was unable to wake him. The couple had been appearing in a New Jersey production of the Gore Vidal play The Best Man.