Mrs Jane O’Brien Dart, who has died aged 90, was a wealthy and influential society hostess, philanthropist, staunch Republican (an intimate of the Reagans) and an art patron and collector. However, for aficionados of 1930s Warner Bros pictures, she was Jane Bryan, the winsome, fresh-faced ingenue who was the innocent foil to the studio’s top gangster stars, James Cagney, George Raft, Edward G Robinson and Humphrey Bogart. She also co-starred in four films with Bette Davis, playing her daughter once (although she was only 10 years younger) and her sister twice.

The first with Davis, who became a close friend, was Marked Woman (1937), Lloyd Bacon’s superb gangster drama. Davis plays a nightclub “hostess”, keeping her profession secret from Bryan as her unworldly college student sister. Bryan brought a touching fragility to the role, especially when she finds herself caught in a web she cannot comprehend, before dying tragically.

In Kid Galahad (1937), the Michael Curtiz film that elevated the boxing movie to more than just a programme filler, Bryan was the virginal sister of fight manager Robinson who falls for one of her brother’s fighters (Wayne Morris). This goads Robinson into almost incestuous jealousy. “We love each other. You can’t keep us apart, you have no reason to,” she pleads. “It’s your own filthy temper and dirty mind. We haven’t done anything wrong.” Davis plays Fluff, Robinson’s girlfriend, who defends Bryan, even though she is in love with the boxer herself.

Bryan was inevitably the blandest of the siblings in Anatole Litvak’s period piece, The Sisters (1938) – the others being Bette Davis and Anita Louise – though she had some good scenes when she discovers her husband (Dick Foran) is fooling around with the local tart. In Edmund Goulding’s The Old Maid (1939), Bryan is good as the spoilt girl brought up by rich widow Miriam Hopkins, not knowing that her real mother is her spinster aunt (Davis). In the final tearjerking scene, Bryan, leaving for her honeymoon, makes a special point of kissing her “Aunt Charlotte” goodbye.

Born in Los Angeles, the daughter of a lawyer, Bryan made her screen debut aged 18 as the disinherited granddaughter of a murdered millionaire in The Case of the Black Cat (1936), a B feature starring Ricardo Cortez as Perry Mason. As a Warner Bros contract player, she went on to make a further 16 features, all but one (These Glamour Girls, MGM, 1939) for Warners, in the next four years. Among them were Confession (1937), in which she played a naive girl once again, fighting for her honour against scoundrel Basil Rathbone; A Slight Case of Murder (1938), as bootlegger Robinson’s pure, finishing-school-educated daughter; and Each Dawn I Die (1939), as Cagney’s girlfriend trying to get him out of prison.

She was the female lead in We Are Not Alone (1939), an allegorical drama based on a James Hilton novel, starring Paul Muni as a married doctor in love with Bryan as a German girl in England at the beginning of the first world war (arguably her finest performance); in Invisible Stripes (1939), in which she tries to keep her fiance William Holden from following his older brother, George Raft, into crime; and in Girls on Probation (1938), in which she played another innocent, unwittingly getting mixed up with criminals until rescued by district attorney Ronald Reagan. It was the first of three films with him, the others being the military school comedies Brother Rat (1938) and Brother Rat and a Baby (1940). The latter was her last film.

On New Year’s Eve 1939, just as her career was going smoothly, with no real highs or lows, she married a businessman, Justin Dart, who would take over the floundering Rexall drug chain in 1945 and build it into Dart-Kraft Inc, a food and consumer products conglomerate. It is doubtful whether she would have become a big star (though there were glimmerings in We Are Not Alone) and the marriage probably came at the right time.

A few weeks after the Darts’ marriage, Reagan married Jane Wyman, his co-star in the Brother Rat movies, and the two couples met for dinner regularly. “At the time, Reagan was a rabid Democrat,” Dart recalled in 1980. “My wife warned me not to talk politics.” By the time Reagan married Nancy Davis, in 1952, he was shifting to the right and the Darts remained part of their inner circle. They were partly responsible for persuading and aiding Reagan to run for governor of California in 1966 and then, in Gore Vidal’s phrase, to become the “acting president”.

After Dart died in 1984, his wife donated their art collection, containing around 70 paintings, to the Monterey Museum of Art, where she served as a trustee. A devout Catholic, she is survived by two sons and a daughter.

• Jane Bryan (Jane O’Brien Dart), actor, born 11 June 1918; died 8 April 2009