Ryan was born in Chicago, Illinois, the first child of Mable Arbutus (Bushnell), a secretary, and Timothy Aloysius Ryan, who was from a wealthy family who owned a real estate firm. He was of Irish (his paternal grandparents were from Thurles) and English descent. Ryan was raised Catholic and educated at Loyola Academy. He graduated from Dartmouth College in 1932, having held the school’s heavyweight boxing title for all four years of his attendance, along with lettering in football and track. After graduation, Ryan found employment as a stoker on a ship that traveled to Africa, a WPA worker, a ranch hand in Montana, and other odd jobs. He returned home in 1936 when his father died, and after a brief stint modeling clothes for a department store, he decided to become an actor.

In 1937 Ryan joined a little theater group in Chicago. The following year he enrolled in the Max Reinhardt Workshop in Hollywood. His role in the 1939 play Too Many Husbands brought an offer from Paramount. Although he had done a screen test for them in 1938 and been turned down as “not the right type”, the studio offered him a $75 a week contract.

In November 1939, Paramount signed Ryan to a six month contract and announced he would play the lead in Golden Gloves (1940), citing his boxing experience at Dartmouth. However, after a screen test with Gloves director Edward Dmytryk, the lead went to Richard Denning and Ryan was cast in a minor, but important role as a boxing “ringer”. He had his first credited role, while making a lasting association with the director in which they would make several films together.

On March 11, 1939, he married Jessica Cadwalader. They had three children: Timothy (b. 1946); Cheyney (b. 1948), a research fellow at Oxford University and a professor of philosophy and law at the University of Oregon; and Lisa (b. 1951). They lived in The Dakota at 72nd and Central Park West in Manhattan and eventually sub-let the apartment to John Lennon and Yoko Ono.

Ryan next appeared in several film noirs: The Secret Fury (1950) with Claudette Colbert directed by Mel Ferrer, and Born to Be Bad (1950) directed by Nicholas Ray. In 1950, the studio bought The Miami Story as a vehicle for him.

In 1951, Ryan was reunited with Crossfire costar Robert Mitchum in The Racket, directed by John Cromwell; that same year, Ray again directed him in a film noir, On Dangerous Ground, with Ida Lupino. Ryan then made the film adaptation of Clash by Night (1952) with Barbara Stanwyck and Marilyn Monroe under Fritz Lang’s direction. According to film critic David Thomson, “at RKO Ryan created the character of a modern neurotic such as the American screen had not dreamed of before.”

Ryan made his television debut in 1955 as Abraham Lincoln in the Screen Director’s Playhouse adaptation of Christopher Morley’s story “Lincoln’s Doctor’s Dog.” As he explained to reporters, despite financial considerations, Ryan preferred to steer clear of any commitment to a TV series:

In the late-1940s, as the House Committee on Un-American Activities (HUAC) intensified its anti-Communist attacks on Hollywood, he joined the short-lived Committee for the First Amendment. Throughout the 1950s, he donated money and services to civic and religious organizations such as the American Civil Liberties Union, American Friends Service Committee, and United World Federalists. In September 1959, he and Steve Allen became founding co-chairs of The Committee for a SANE Nuclear Policy’s Hollywood chapter.

Ryan never appeared in Gene Roddenberry’s Star Trek, but he was considered for the role of Commodore Matt Decker in the 1967 episode “The Doomsday Machine”. Episode author Norman Spinrad had written the script with Ryan in mind to play Commodore Decker, but Ryan had prior commitments. That role went to William Windom.

In 1970 Ryan discovered he had inoperable cancer of the lymph glands (he was a smoker). He decided to keep working, and said, “I’ve had a good shot at life.”

In April 1971, Ryan returned to the stage to play James Tyrone in Arvin Brown’s critically acclaimed Off-Broadway production of Long Day’s Journey into Night.

He originally refused the lead in Lolly-Madonna XXX (1973) with Rod Steiger because he wanted to take his wife to Europe, but she died of cancer in May 1972, and he ended up playing the part. “Something very big is missing and I don’t know what to put in its place,” he said.

Robert and Jessica remained married until her death from cancer in 1972. He died from lung cancer in New York City the following year at age 63.

Ryan’s final roles included: The Man Without a Country (1973), a TV movie for Delbert Mann; The Outfit (1973) with Robert Duvall; Executive Action (1973) with Lancaster, from a script by Dalton Trumbo; and a version of The Iceman Cometh (1973) with Lee Marvin and director Frankenheimer. Ryan, who died before the latter’s premiere, won the Kansas City Film Critics Circle Award for Best Supporting Actor, the National Board of Review Award for Best Actor (in a tie with Al Pacino, for Serpico), and a special award from the National Society of Film Critics. The Iceman Cometh and Executive Action both were released in November 1973, after Ryan’s death.