Hill began acting in college in his native Canada and in Seattle before moving to England in 1948 to pursue professional opportunities there. He made his London stage debut in "Home of the Brave" (1948), an at the time hard-hitting drama about a black soldier's abuse at the hands of his fellow white GIs. In quick succession, he landed other stage roles in "The Male Animal", "Man and Superman", and "The Matchmaker" as well as making his English screen debut in a small role in "Miss Pilgrim's Progress" (1950). He was brought to Broadway in 1955 to recreate his role in "The Matchmaker" and stayed on to perform in such classics of the New York stage as Thomas Wolfe's "Look Homeward, Angel" and "The Gang's All Here", with Melvin Douglas. But it was the role of the hard-drinking college professor George who confronts his shrewish wife Martha (Uta Hagen) in Edward Albee's "Who's Afraid of Virginia Woolf?" that made him a Broadway force to reckon with.
Hill made his US screen debut in the medical drama "The Young Doctors" (1961) and began essaying regular supporting roles. He played chief aide to Marlon Brando's ambassador in the partially successful Cold War drama "The Ugly American" (1963), was George C. Scott's well-meaning pal in one of the 1960s finest films, "Petulia" (1968) and starred as a medical specialist in the uneven sci-fi thriller "The Andromeda Strain" (1971). Sam Peckinpah cast him as a government official running covert operations in "The Killer Elite" (1975), and he played a theme park executive in the sequel "Futureworld" (1976) and a field medic in the uneven war drama "A Bridge Too Far" (1977).
Hill made his small screen debut in a TV remake of the hit movie "Born Yesterday" (1956) as a writer whom a wealthy junk dealer hires to educate his sassy girlfriend. He soon became a regular player on TV dramas ("The Desperate Hours" 1967, "The Other Man" 1970) and anthology series ("Great Ghost Tales" 1961, "Tales of the Unexpected" 1979). He landed his own popular courtroom series "Owen Marshall: Counselor at Law" (ABC, 1971-74) as a compassionate defense attorney practicing in a small California town, and was the publisher of a PEOPLE-style magazine on the series "Glitter" (ABC, 1984-85).