Disney
MacArthur was selected by Walt Disney to star in The Light in the Forest (1958), playing a white man raised by Indians. In April 1957, he signed a three-picture deal with Disney. For Light in the Forest he was paid $2,500 per week, which increased to $3,000 per week for the second film and $3,500 for the third. However, MacArthur was only available to work during his summer vacation from Harvard, where he was studying history.
Disney executives liked his performance and cast him in Third Man on the Mountain (1959), playing a young man who climbs the Matterhorn. His mother had a cameo role.
Deciding to make acting his full-time career, he left Harvard in his second year to appear in two more Disney movies, Kidnapped (1960) and Swiss Family Robinson (1960). He was named a possibility for Bon Voyage (1962) but did not appear in the film.
MacArthur made his Broadway debut in 1960 playing opposite Jane Fonda in Invitation to a March, for which he received a Theatre World Award. Although he never returned to Broadway, he remained active in theater throughout his career, appearing in such productions as Under the Yum Yum Tree, The Moon Is Blue, John Loves Mary (with his wife Joyce Bulifant), Barefoot in the Park and Murder at the Howard Johnson's.
He also released several records in the early 1960s, scoring two minor hits with "(The Story of) The In-Between Years" and "The Ten Commandments of Love", which peaked at number 94 on the Billboard Hot 100 in 1963.
MacArthur delivered a chilling performance as baby-faced opium dealer Johnny Lubin in The Untouchables episode "Death For Sale". He also appeared in episodes of the television shows Bus Stop and Wagon Train. He returned to feature films as one of several young actors in The Interns (1962), Columbia's popular medical drama.
He appeared in episodes of The Dick Powell Theatre, Sam Benedict and Arrest and Trial, then made Spencer's Mountain (1963) at Warner Bros. with Henry Fonda and Cry of Battle (1963) in the Philippines.
In 1963, MacArthur was nominated for the Top New Male Personality category of the Golden Laurel Awards. That year, he starred in and produced a pilot for a television series about a writer, Postmark: Jim Fletcher, but it was not sold.
He guest-starred on the television shows Burke's Law, The Eleventh Hour, The Great Adventure, and The Alfred Hitchcock Hour before appearing in the feature films The Truth About Spring and The Bedford Incident, both in 1965.
In Battle of the Bulge (1965), MacArthur again played the role of a young and inexperienced officer. He appeared in Ride Beyond Vengeance (1966) and guest-starred on Branded, Combat!, Gunsmoke, Hondo, Insight, Death Valley Days, Bonanza, The Virginian, Twelve O'Clock High and Tarzan.
MacArthur returned to Disney to appear in Willie and the Yank (1967) for television, released theatrically as Mosby's Marauders. He also had a role in The Love-Ins (1967) for Sam Katzman and a brief but memorable appearance in the Clint Eastwood film Hang 'Em High (1968) as a preacher.