Cregar quickly rose to stardom, appearing in a variety of genres from film noir to screwball comedy to horror movies.

He was a popular actor at the time of his death in 1944 at age 31, a result of complications from binge dieting undertaken to suit him for leading man roles.

[14] He spent a year in 1934/35 as a cadet in the Merchant Marine[15] and then acted in productions of the Hedgerow Theater, an amateur company in Rose Valley, Pennsylvania.

[6][17] In 1936, Cregar persuaded the Philadelphia Rotary Club to support him with a $400 loan to study acting and gain on-stage experience at California's Pasadena Playhouse, where he remained for about two years without being noticed.

[18] He later said Thomas Browne Henry of the Playhouse gave him the best advice he possibly could, telling him "not to lose a pound of weight, but instead to develop a thin man's personality".

[19] Returning to Pennsylvania, he appeared in small roles for little money in several productions mounted by the Federal Theatre at Bryn Mawr College's Goodhart Hall.

"[21] He kept his role when the leads were replaced for a new production that hoped to reach Broadway, but he appeared only in Pasadena and San Francisco before the show closed.

[22] Cregar made his film debut with a pair of uncredited appearances as a court clerk in Granny Get Your Gun (1940) and as a mechanic in Oh Johnny, How You Can Love (1940).

[9][24] Impressed that the English actor Robert Morley–a man his own height and girth–had scored a triumph onstage in the play Oscar Wilde in both London in 1936 and in New York in 1938, Cregar determined to duplicate that success.

They announced him for The Californian,[30] which was not made, but Cregar was then cast in the big-budget historical movie Hudson's Bay (1941),[31] where opposite Paul Muni he appeared "mountainous".

Cregar appeared opposite Veronica Lake and Alan Ladd[39] as the "unctuous, deceitful epicure" who double crosses his hired gun.

[41] Finally, his busy 1942 ended with The Black Swan (1942), a childish fantasy of swashbuckling pirates in which Cregar "bellows oaths like an irate opera singer" opposite Tyrone Power and Maureen O'Hara.

[48] Hoping to escape being typecast as a villain in his next film, Cregar got Fox to buy the rights to a recent best-seller, Patrick Hamilton's Hangover Square, published in the U.S. in 1942.

This prompted Darryl Zanuck to arrange for an article in Silver Screen to link Cregar romantically with Dorothy McGuire and to report that, despite his weight, the actor had female fans.

[60] Gossip columnists reported Cregar had a crush at one time or another on Linda Darnell or Dorothy McGuire,[61] or was dating Renie Riano, an older actress,[62] or linked him romantically to Van Johnson.

[65] The crash diet that Cregar followed for his roles in The Lodger and Hangover Square (which included prescribed amphetamines) placed a strain on his system, resulting in severe abdominal problems.

At the time of his death, his next scheduled film was an adaptation of Les Misérables directed by John Brahm,[71] and Billy Rose wanted him to star in a Broadway production of Henry VIII.

[75] On February 8, 1960, Cregar received a posthumous star on the Hollywood Walk of Fame at 1716 Vine Street for his contributions to the film industry.