Following his advice to "do what you love," she attended Northwestern University graduating in 1980, where she was a member of the Alpha Chi Omega sorority and earned a degree in theater.

Other major stage credits include Two Shakespearean Actors with Eric Stoltz at Lincoln Center, Our Town at the Seattle Repertory Theatre, and Three Sisters at the La Jolla Playhouse in San Diego.

In 1989, Innes played Miss Andrews in the Nickelodeon sitcom Hey Dude in the second season episode "Teacher's Pest".

In January 2007, Innes left ER in the middle of the thirteenth season, becoming the longest-serving cast member in the show's history, but Noah Wyle appeared in four more episodes than her.

On May 7, 2010, NBC announced that Innes would be co-starring in the short-lived science fiction/mystery/action/thriller drama The Event as Sophia, "the leader of a mysterious group of detainees" with Lisa Vidal, who played Kerry Weaver's wife, Sandy Lopez, in the eighth, ninth and tenth seasons of ER.

[citation needed] In 2006, Innes told the Daily Mirror that ten years of portraying Dr. Weaver's limp had caused her to experience the early stages of actual spinal damage ("the bottom of my spine is starting to curve on one side from 10 years of raising my hip"), and as a consequence, ER's producers introduced a plot arc in which Weaver's disorder was surgically corrected.