[11] There, in 1928, radio pioneer Fred Smith had created the program Newscasting, which in 1931 evolved into the popular national news series, The March of Time.

[12] For 13 months Stewart worked in all aspects of radio production at WLW – acting, announcing, directing, producing, writing and creating sound effects.

"[13]: 10 In March 1935 Stewart saw Welles's stage performance in Archibald MacLeish's verse play Panic, and recommended him to director Homer Fickett.

[14]: 86 "It was like a stock company, whose members were the aristocrats of this relatively new profession of radio acting," wrote fellow actor Joseph Julian.

At that time Julian had to content himself with being an indistinguishable voice in crowd scenes, envying this "hallowed circle" that included Stewart, Welles, Kenny Delmar, Arlene Francis, Gary Merrill, Agnes Moorehead, Jeanette Nolan, Everett Sloane, Richard Widmark,[15]: 9  Art Carney, Ray Collins, Pedro de Cordoba, Ted de Corsia, Juano Hernandez, Nancy Kelly, John McIntire, Jack Smart and Dwight Weist.

[20]: 390  In addition to playing a number of roles in the drama series and its sponsored continuation, The Campbell Playhouse, Stewart made significant contributions to the celebrated broadcast, "The War of the Worlds", as rehearsal director, actor and co-writer.

[22]: 195 [23] On January 14, 1939, in Arlington, Virginia, Stewart married actress and singer Peg LaCentra (1910–1996), a vocalist with Artie Shaw's first orchestra who worked in radio, films and television.

[32] He worked under John Houseman at the newly created Voice of America (1942–1943), broadcasting news, editorials and commentary from the U.S. press, and quotes from notable speeches, to audiences in Europe.

[34] After the war Stewart went to work for David O. Selznick and Dore Schary as a writer, director and producer, and directed screen tests for Paramount Pictures.

[31] Stewart's many feature film credits as an actor include The Window, Champion, Twelve O'Clock High, Deadline – U.S.A., The Bad and the Beautiful, The Juggler, Kiss Me Deadly, King Creole, In Cold Blood, The Day of the Locust and W.C. Fields and Me, in which he portrayed Florenz Ziegfeld.

[35] On television, Stewart's director credits include the syndicated series Top Secret (1954–1955), in which he costarred with the young Gena Rowlands, and a notable episode of The Twilight Zone, "Little Girl Lost" (1962).

He was host, narrator and actor in the syndicated series Deadline (1959–1961) and appeared in episodes of The Ford Theatre Hour, Suspense, Playhouse 90, Alcoa Theatre, Alfred Hitchcock Presents, The Asphalt Jungle, Perry Mason, Dr. Kildare, Mannix, Mission Impossible, The Name of the Game ("L.A. 2017"), McMillan & Wife, Columbo, The Rockford Files, Lou Grant and Remington Steele, among many other TV series.

Orson Welles called upon Stewart to play a role in his film The Other Side of the Wind, shot in the 1970s and left unfinished until its release in 2018.

[22]: 195, 297 Stewart died at the age of 77 of heart failure at Cedars-Sinai Medical Center in Los Angeles on February 17, 1986, after a long illness.