A veteran character player often cast as tough military men or salt-of-the-earth small town Americans, Ryan decided to pursue an acting career after a stint in the special services entertainment unit of the US Navy during the Korean War. He briefly appeared in "Thunder Road" (1958), with Robert Mitchum and then moved to NYC to work for over twenty years on stage and TV. Alternately billed as Mitch or Mitchell Ryan, he made his stage debut in "Whisper to Me" (1960) before joining Joseph Papp's New York Shakespeare Festival in 1962. He played the title role in "Baal" and landed a key role opposite Lee Remick in the thriller "Wait Until Dark" (1966). Among his other stage credits are Eugene O'Neill's "A Moon for the Misbegotten" (1968), "Medea" (1982) and appearances with the Arena Stage in Washington, DC (1969-70).
Ryan landed a regular TV gig as Burke Devlin on the Gothic daytime drama "Dark Shadows" (ABC, 1966-70). Producer Jack Webb then hired him to play one of the leads in the police drama "Chase" (NBC, 1973-74). Ryan went on to appear in several, mostly short-lived, series: "Executive Suite" (CBS, 1976-77); "Having Babies/Julie Farr, M.D." (ABC, 1978-79); "The Chisholms" (CBS, 1980), replacing Robert Preston as the patriarch; "King's Crossing" (ABC, 1982); and "High Performance" (ABC, 1983). He has also made numerous appearances in TV-movies and miniseries since the early 1970s. Among his more notable vehicles are "The Entertainer" (NBC, 1976), with Jack Lemmon, "North and South" (ABC, 1985), "Robert Kennedy and His Times" (CBS, 1985), as Robert McNamara, "Death of a Centerfold: The Dorothy Stratton Story" (NBC, 1981), as Hugh Hefner, "Fatal Vision" (NBC, 1979), "Margaret Bourke White" (TNT, 1989), as General Patton, and "Gramps" (NBC, 1995), with Andy Griffith.
Ryan returned to the big screen in "Monte Walsh" (1970) but his career has been sporadic since. Throughout the 1970s, he played small supporting roles in such features as Clint Eastwood's "High Plains Drifter", Peter Yates' "The Friends of Eddie Coyle" and "Magnum Force" (all 1973). After over a decade, he returned to features as a Vietnam veteran whose drug operation is the target of investigation by Mel Gibson and Danny Glover in Richard Donner's "Lethal Weapon" (1987). He gave a strong performance as the patriarch of a mountain family in Ted Kotcheff's "Winter People" (1989) and executed a deft, but rare, comic turn in Jim Abrahams' "Hot Shots! Part Deux" (1993). Ryan offered support to Jessica Lange and Tommy Lee Jones in the late Tony Richardson's "Blue Sky" (filmed in 1990; released in 1994) and was one of the candidates in "Speechless" (also 1994). In 1995, he was featured in both "Malicious" and "Judge Dredd".