In the 1940s he also began to perform in films, when he reprised his role from the hit Broadway play, The Little Foxes, in the William Wyler movie of the same name, starring Bette Davis.

In 1936 he appeared in a production of Sweet River, an adaptation of Harriet Beecher Stowe's Uncle Tom's Cabin at the 55th Street Theater.

Marriott would also appear in regional theater productions, as he did in a 1944 version of Elena Miramova's play, Dark Eyes in Stamford, Connecticut.

[14] Also in 1946 he originated the role of Joe Mott, one of the major parts in the Eugene O'Neill classic, The Iceman Cometh, which opened at the Martin Beck Theatre on October 9.

The two one-acts previewed at the New Stages Theater in Greenwich Village, prior to opening on March 16 at the Cort and running for 318 performances, closing on December 18, 1948.

[20] In September 1948, when Rex Ingram was arrested for violating the Mann Act, Marriott replaced him in the lead in Charleston 1822, a drama by Dorothy Heyward which was in previews in New Haven, Connecticut.

[22] In 1949, Marriott was cast as one of the leads, Arrafi, in the Barrie Stavis drama, The Sun and I, which opened on March 20 at the New Stages Theater in Greenwich Village.

[28] In 1951, Marriott had a supporting role in a revival of the Pulitzer Prize-winning play, The Green Pastures, which also co-starred Alonzo Bosan and Ossie Davis, all of whom received positive reviews for their performances.

[29][30] That same year, Marriott would appear in the George S. Kaufman play, The Small Hours, which had a short run at the National Theatre in February and March.

[31][32] On the small screen that year, his performances included the season finale episode of the Westinghouse Summer Theater, entitled "The Guinea Pigs".

[36] As part of the DuMont Television Network's anthology series, One Man's Story, Marriott portrayed the title character in "The Ordeal of Frederick Douglass".

[37] His performance in "The Challenge", a story by Jerome Coopersmith, on CBS Television's Lamp Unto My Feet program, was given very positive reviews, with one source stating that he "... gave one of the finest characterizations of his career.