He landed jobs as an extra in short films produced by Paramount Pictures in its Long Island studio, and also performed with several stock theater companies, culminating with playing the male lead in the 1929 Broadway musical Sweet Adeline.

In 1945, having not worked for a major studio for five years, he was selected by director Elia Kazan for the role of Johnny Nolan, the dreamy alcoholic father in A Tree Grows in Brooklyn (1945), which earned him the Academy Award for Best Supporting Actor.

He had a regular role in the hit sitcom It's a Great Life from 1954 to 1956, and guest-starred in dozens of episodes of popular television series from the 1950s through mid-1960s.

[2] His parents, Ralph H. Dunn (c. 1875–1943), a member of the New York Stock Exchange,[3] and mother Jessie L. Archer (c. 1871–1946)[4] had married in January 1901.

[6][7] In December 1905, while wintering with his parents at Shippan Point, Connecticut, the four-year-old Dunn had a near-accident, reported in The New York Times, when a bulldog belonging to his babysitter lunged at him.

[16] Upon his return to New York, he landed the male lead in the touring company of the musical Sweet Adeline, opposite Helen Morgan.

A Fox Film employee asked if they could also test Dunn, and had him read a scene from the stage production of Bad Girl.

While MGM was not impressed with their result, Fox director Frank Borzage liked Dunn's screen test and wanted to cast him in his upcoming film version of Bad Girl.

[18] Dunn signed a film contract with Fox a few days later and relocated to Hollywood;[12][18] his mother came to live with him the following year.

[1][4] Dunn made his screen debut in Bad Girl (1931),[19] which catapulted him and co-star Sally Eilers to "overnight fame".

[20] The Los Angeles Times called Dunn's star turn "triumphant", asserting that "no performance has lately equaled the impression made by this rather plain young man, who, aside from having a likable personality, scores a major hit by his ability as an actor".

[21] Fox immediately re-teamed Dunn and Eilers in Over the Hill (1931), followed by Dance Team (1932), Sailor's Luck (1933), and Hold Me Tight (1933).

He was about to start filming a remake of The Song and Dance Man, but the project was shelved due to Fox's merger with Twentieth Century Pictures.

[39] With musicals on the wane in the late 1930s, Dunn's career slumped as he found roles in a series of "mediocre comedies and melodramas".

[40] According to Dorothy Lee, who worked alongside him on Take a Chance (1933), Dunn and co-star Lillian Roth took turns getting drunk during the production.

[41] During the filming of George White's 1935 Scandals, shooting started in the late morning to accommodate Dunn and other members of the cast who frequently imbibed.

[37][44] In 1940, Dunn returned to Broadway for an 87-week run[45] in the hit musical Panama Hattie with Ethel Merman, to positive reviews.

[7][12] Dunn had not worked for a major studio for five years when he was called in to screen-test for the role of Johnny Nolan, the dreamy alcoholic father in the 20th Century Fox production A Tree Grows in Brooklyn (1945).

[7] However, a friend, actress and dancer Gloria Grafton, urged casting directors involved in the extensive talent search to hire him.

In the radiant performance by these two actors of a dreamy adoration between father and child is achieved a pictorial demonstration of emotion that is sublimely eloquent.

[12] In 1947, largely on the basis of his performance in A Tree Grows in Brooklyn, Dunn was cast as Jamie Tyrone, a man who resorted to drink to forget his unhappy past, in Eugene O'Neill's semi-autobiographical play A Moon for the Misbegotten.

[58] The production budget was increased by 10% to enable dress rehearsals to take place in New York rather than in the first out-of-town tryout in Columbus, Ohio, in order to accommodate Dunn's poor health.

[52] He guest-starred in dozens of episodes of popular television series in the 1950s through mid-1960s, including Bonanza, Rawhide, Route 66, Ben Casey, and The Virginian.

[68] In 1962, Dunn played a clown in full makeup and costume in an episode of Follow the Sun, and sang "On the Good Ship Lollipop" from his 1934 film Bright Eyes.

[69] In 1963 he played the character of P. J. Cunningham, the manager-driver for a music band led by Bobby Rydell, in the unsold Desilu half-hour television pilot Swingin' Together.

[14] On the set of Hold Me Tight (1933), he insisted on filling in for an extra who was going home sick and who had confided to Dunn that he could not afford to lose his day's pay of $7.50.

[82] Dunn awarded the second prize to a woman from Fort Beaufort, South Africa, and sent runner-up gifts to three other American women.

[86] On Christmas Day 1937, Dunn and his fiancée, 17-year-old actress Frances Gifford, flew in his plane to Yuma, Arizona, to be married in a Presbyterian church there and afterwards returned to Hollywood.

His mother took charge of his finances and invested most of his earnings in stocks, bonds, real estate, and trust funds, giving him a weekly allowance.

[83] Thereafter Dunn lost a $40,000 option on a play, Cock of the Walk, that failed to reach Broadway,[12][90] as well as thousands of dollars in the stock market.