Marshall made his film debut in the fine thriller "The House on 92nd Street" (1945) and subsequently appeared in several other memorable film noirs, "Call Northside 777" (1948) and "Pushover" (1954), before landing a supporting role in "The Caine Mutiny" (1954). His breakthrough role was the Fourth Juror in Sidney Lumet's "Twelve Angry Men" (1957). He played the stuffy, buttoned-down, and bespectacled member of the ensemble, a man so cool and dispassionate that he doesn't even break a sweat in the sweltering jury room. Marshall shone again amid an impressive ensemble that same year in "The Bachelor Party", a sensitive Paddy Chayefsky teleplay given the feature treatment.
Marshall is primarily known for his major career in TV, having amassed over 80 credits over the course of his more than four decades in the medium. He was a staple performer in live dramas and anthology series of the late 40s and 50s including "Lights Out", "Kraft Television Theater", "Actors Studio", "Philco Television Playhouse" and "Shirley Temple's Storybook". He is probably best remembered as trial lawyer Lawrence Preston on the classic TV drama, "The Defenders" (CBS, 1961-65), a role that won him back-to-back Emmy awards for Best Actor in 1962 and 1963. Based on an original story by playwright Reginald Rose ("Twelve Angry Men"), this landmark legal series featured Marshall and Robert Reed as a father-son lawyer team who sometimes tackled cases involving issues that remain controversial to this day (e.g., abortion, euthanasia, blacklisting). Marshall returned to series TV just a few years later for another long comfortable run as Dr. Craig, the illustrious physician protagonist in "The Doctors" (NBC, 1969-73) segments of "The Bold Ones".
After playing dignified responsible characters for most of his earlier years, Marshall displayed an obvious glee when he was able to ham it up in some of his later roles. He was delightful as Upson Pratt, a vicious multimillionaire who experiences a serious roach problem during a NYC blackout in a memorably gross segment of George Romero's "Creepshow" (1982). He also did a zesty TV guest shot on Romero's "Tales from the Darkside", in a fairly sick episode entitled "The Grither", playing a father who shakes up his jaded kids with a scary Christmas story about a "mythical" monster.
Marshall remained a vital TV figure into his 80s, appearing in such high profile fare as "Stephen King's 'The Tommyknockers'" (ABC, 1993) and "Oldest Confederate Widow Tells All" (CBS, 1994). He returned to the hurly-burly of a weekly series as an ensemble player on the ambitious medical drama "Chicago Hope" (CBS, 1994). Marshall's enviable experience lent ample credibility to the role of Dr. Arthur Thurmond, a "legendary" surgeon who wields much power with the hospital administration. He returned to features in the key role of John Mitchell in "Nixon" (1995) and later played a wealthy businessman with a much younger wife in Clint Eastwood's "Absolute Power" (1997).