An actor who was on the precipice of superstardom when Manhattan prosecutors accused him of assaulting his then-girlfriend is set to go on trial Wednesday, seeking to keep his career alive in an unusual proceeding that is expected to attract national attention.

The actor, Jonathan Majors, was charged in March with misdemeanor assault and harassment. Prosecutors say he attacked the woman, Grace Jabbari, during a car ride to his home, slapping her face, grabbing her hand violently and, after she got out the vehicle, throwing her back into it.

The arrest froze Mr. Majors’s rapid ascent in the film industry, where he was poised to anchor several Marvel movies and awaiting the wide release of a star vehicle, “Magazine Dreams,” which is now in limbo. While it is unusual for a misdemeanor assault charge to go to trial — the vast majority of defendants plead guilty to avoid risking a harsher sentence — Mr. Majors is fighting to prove his innocence and to salvage his reputation in Hollywood.

His lawyer, Priya Chaudhry, has been aggressive in defending him, calling Ms. Jabbari a liar who attacked Mr. Majors.