He originated the role of Marshal Matt Dillon for the radio series Gunsmoke (1952–1961) and narrated the television adventures of Rocky and Bullwinkle (1959–1964) and The Fugitive (1963–1967).

Finding fewer onscreen roles in the 1950s, he changed from actor to producer-director with television work, narration, and a series of Warner Bros. films in the 1960s.

The family moved to Southern California where, as William Cann, he attended Excelsior Union High School in Norwalk.

He majored in drama and literature at Fullerton College, in Orange County, California, and began his career as an announcer, writer, and director for Los Angeles radio station KMPC.

[7] At KMPC, the 22-year-old Conrad produced and acted in The Hermit's Cave (c. 1940–44), the Los Angeles incarnation of a popular syndicated horror anthology series created at WJR Detroit.

[21] He played newspaper editor Walter Burns opposite Dick Powell's reporter Hildy Johnson in the ABC radio drama The Front Page (1948).

[26] Most prominently, Conrad's deep, resonant voice was heard in the role of Marshal Matt Dillon on CBS Radio's gritty Western series Gunsmoke (1952–1961).

The producers originally rejected him for the part because of his ubiquitous presence on so many radio dramas and the familiarity of his voice, but his impressive audition could not be dismissed, and he became the obvious choice for the role.

[27] When Gunsmoke was adapted for television in 1955, executives at CBS did not cast Conrad or his radio costars despite a campaign to get them to change their minds.

[29] Conrad directed and narrated the 1957 episode "Epitaphs", an adaptation of Edgar Lee Masters's poetry volume Spoon River Anthology.

Standing 11.5 in (29.2 cm) high and weighing 45 lb (20.4 kg), the figurine had been slashed during the making of the film by Sydney Greenstreet's character Kasper Gutman, leaving deep cuts in its bronze patina.

[37] Late in life, Conrad narrated the opening and closing scenes of the 1991 Bruce Willis feature film Hudson Hawk.

His voice is heard in the Clio Award-winning 1971 public-service announcement about pollution featuring Iron Eyes Cody, created for Earth Day by Keep America Beautiful and the Ad Council.

His other credits as a director include episodes of The Rifleman, Bat Masterson, Route 66, Have Gun – Will Travel, 77 Sunset Strip, Temple Houston and Ripcord, as well as ABC's crime drama Target: The Corruptors!.

[46] In 1980, Conrad married Tipton "Tippy" Stringer (1930–2010), a TV pioneer and the widow of NBC newscaster Chet Huntley.

Having been known for his prowess using light tackle, as documented in the magazine Field & Stream, on May 23, 1972, in the Yucatán Channel of Mexico, Conrad caught a 62 lb, 4 oz sailfish on thread-like 6-lb-test line.