Born Morris Nussbaum in Danville in Vermilion County in eastern Illinois, Ankrum originally began a career in academics. After graduating from The University of Southern California with a law degree, he went on to an associate professorship in economics at the University of California, Berkeley. While at Berkeley he became involved in the drama department and eventually began teaching drama and directing at the Pasadena Playhouse.
From 1923 to 1939, he acted in several Broadway stage productions, including Gods of the Lightning, The Big Blow and Within the Gates.
Before signing with Paramount Pictures in the 1930s, Nussbaum had already changed his last name to Ankrum. Upon signing with the studio, he chose to use the name “Stephen Morris” before changing it to Morris Ankrum in 1939.
Ankrum's stern visage and sharply defined features helped cast him in supporting roles as stalwart authority figures, including scientists, military men (particularly army officers), judges and even psychiatrists in more than seventy films, mostly B movies. One standout role was in Metro-Goldwyn-Mayer's production of Tennessee Johnson (1942), a biographical film about Andrew Johnson, the 17th U.S. president. As Senator Jefferson Davis Ankrum movingly addresses the United States Senate upon his resignation to lead the Confederate States of America as that republic's first - and only - president. Ankrum's film career was extensive and spanned thirty years. His credits were largely concentrated in the western and science fiction genres.
Ankrum appeared in such westerns as Ride 'Em Cowboy in 1942, Vera Cruz opposite Gary Cooper and Burt Lancaster, Apache (1954), and Cattle Queen of Montana with Barbara Stanwyck and Ronald Reagan.
In the sci-fi genre, he appeared in Rocketship X-M (1950), Flight to Mars (1951), as a Martian, Red Planet Mars (1952), playing the United States Secretary of Defense; the cult classic Invaders From Mars (1953), playing a United States Army officer; and as an Army general in Earth vs. the Flying Saucers (1956). In 1957, he played a psychiatrist in the cult sci-fi classic Kronos and had military-officer roles in Beginning of the End and The Giant Claw.
By the end of 1958, Ankrum's film career had essentially ended, though he continued taking television roles. In the syndicated series, Stories of the Century, Ankrum played the outlaw Chris Evans, who with his young associate, John Sontag, played by John Smith, turned to crime to thwart the Southern Pacific Railroad, which Evans and Sontag held in the contempt consistent with the theme of Frank Norris's muckraking novel, The Octopus: A Story of California.
Ankrum made twenty-two appearances on CBS's Perry Mason as one of several judges who regularly presided over the murder trials of Mason's clients from the show's first season in 1957 until his death in 1964. The show ended two years later.
Ankrum appeared in westerns The Adventures of Rin Tin Tin, Bronco, Maverick, Tales of the Texas Rangers, Cimarron City, Rawhide and The Rifleman.
On October 15, 1957, Ankrum had a major part in the episode “Strange Land” of the ABC/Warner Brothers western Sugarfoot, starring Will Hutchins. Ankrum played an embittered rancher named Cash Billings, who allows a hired gunman, Burr Fulton, portrayed by Rhodes Reason, to take over his spread, but Sugarfoot arrives to bring law and justice to the situation. Jan Chaney appears in the episode as Billings' daughter, Anne, who takes a liking to Sugarfoot. Ankrum appeared again, as John Savage in 1959, in the Sugarfoot episode “The Wild Bunch”. In 1961, he again played an embittered and this time paralyzed rancher, Cyrus Dawson, in the episode “Incident at Dawson Flats” of the ABC/WB western series, Cheyenne, with Clint Walker in the starring role, with other guest-starring parts for Jock Gaynor, Joan O'Brien, Gerald Mohr, and Hampton Fancher.
In the 1958-1959 season, Ankrum appeared twelve times in Richard Carlson's syndicated western series Mackenzie's Raiders, along with other cast “Raiders” Brett King, Jack Ging, and Louis Jean Heydt. In the series set on the Rio Grande border, Carlson plays Colonel Ranald Mackenzie, who faces troubles from assorted border outlaws.
Ankrum was cast in an episode of the 1959 CBS sitcom Dennis the Menace.
He also made occasional uncredited appearances in several Roger Corman films. While involved in films and television, Ankrum was still involved in live theatre and continued to direct plays at the Pasadena Playhouse.
He and his second wife, Joan Wheeler, had a child, David Ankrum, best known as Adam from Tabitha. David Ankrum eventually became a Hollywood agent.
On September 2, 1964, Ankrum died of trichinosis. At the time of his death, he was still involved with Raymond Burr's Perry Mason series. His final appearance on Perry Mason, “The Case of the Sleepy Slayer,” and his last film, Guns of Diablo, in which he was cast as Ray Macklin, were released in 1964 and 1965, respectively, after Ankrum's death.
Ankrum's remains are interred at Spring Hill Cemetery in Danville, Illinois.