She was best known for her roles as Mavis Anderson in the CBS prime time soap opera Dallas and as Lois Morgan, the mother of the title character on the ABC sitcom Ellen.

In 1977, she appeared in made-for-television movies The Death of Richie, Alexander: The Other Side of Dawn, and Having Babies II, and the following year co-starred opposite Cicely Tyson in A Woman Called Moses.

From 1982 to 1988, Hirson played the recurring role of Mavis Anderson, friend and confidante of Miss Ellie Ewing (Barbara Bel Geddes) in the CBS prime time soap opera, Dallas.

She also had recurring roles on Murphy Brown and The Secret Life of the American Teenager, and guest-starred on Law & Order, ER, NYPD Blue, Judging Amy, Just Shoot Me!, and Cold Case.

She also appeared in Private Benjamin, Revenge of the Nerds, Mass Appeal, Blind Date, Bride of Boogedy, The Big Picture, The Glass House, and The Lost.