Born in New York City, McNally attended Fordham University School of Law and was an attorney in the late 1930s before he pursued his passion for acting. He was a one time president of the Catholic Actors Guild. He started his stage career using his real name Horace McNally and began appearing uncredited in many World War II-era films. In 1948, he changed his stage name to Stephen McNally (taking the name of his then-2-year-old son)[3] and began appearing credited as both movie villains and heroes. In 1940, he had a leading role in the stage version of Johnny Belinda. He played menacing roles in such films as Johnny Belinda (1948) and the James Stewart western Winchester ’73 (1950). He co-starred in the Burt Lancaster film noir Criss Cross (1949). Other notable 1950s films included No Way Out (1950), Split Second (1953), and Johnny Rocco (1958). McNally was cast in three episodes of the ABC religion anthology series Crossroads. He portrayed Monsigneur Harold Engle in “Ringside Padre” (1956) and Father Flanagan of the Boys Town orphanage in Nebraska in “Convict 1321, Age 21” (1957). In between, he was cast as United States Army General George S. Patton, Jr., in “The Patton Prayer” (also 1957). McNally also co-starred on the “Ben Courtney Story” episode of Wagon Train as a former Union soldier turned Sheriff in 1958. In 1959, he portrayed Clay Thompson, a bounty hunter, with Myron Healey as a sheriff, in the CBS western series, The Texan, starring Rory Calhoun.

McNally was thereafter cast in the 1960 episode “Moment of Fear” of the CBS/Four Star Television anthology series, The DuPont Show with June Allyson, with episode co-stars Edgar Bergen and Darryl Hickman. Thereafter, he appeared in the NBC anthology series, The Barbara Stanwyck Show, and in the Darren McGavin western series, Riverboat. In 1961, he portrayed the part of Sky Blackstorm in the episode “Incident of the Blackstorms” on CBS’s Rawhide. In the 1961–62 season, McNally and Robert Harland had their own crime drama on ABC, another Four Star Production called Target: The Corruptors!. The program aired on Friday in a good time slot after the popular 77 Sunset Strip, but it failed to gain renewal for a second season. McNally played a crusading newspaper reporter in the series, with Harland was his undercover agent. During the 1970s, McNally guest starred in television programs such as Fantasy Island and James Garner’s The Rockford Files and Police Story. McNally died of a heart attack June 4, 1994, at age 82, at his home in Beverly Hills, California. He was survived by his wife, Rita, eight children and eight grandchildren.