[W]hen NewsRadio got canceled, ... I thought, there's probably not gonna be something like [that show] again for me... So then, when ER called ... that was a way to stay in [television] that would remain interesting for me.
After appearing in several plays, Tierney moved to Los Angeles, California, and in 1987 got her first break with a role in Disney's made-for-TV film Student Exchange. Tierney's first starring role in a film was in a low-budget independent film called Dead Women in Lingerie, shot in 24 days. The film never received a theatrical release, although it was released on DVD in 2005.
Tierney married actor and Director Billy Morrissette on February 1, 1993, two days before her 28th birthday, after the two met on the set of a never-aired television series. After being married for 13 years, she filed for divorce in 2006, citing irreconcilable differences. They had no children.
Tierney had a number of small roles in film and television but first received regular national exposure with her leading role in the sitcom NewsRadio from 1995 to 1999. While she was a NewsRadio cast member, she also appeared in several successful films, including Primal Fear, Primary Colors, Forces of Nature, Welcome to Mooseport, and Liar Liar opposite Jim Carrey.
From 1999 to 2008, Tierney played Nurse Abigail "Abby" Lockhart on ER, a character that began as a guest appearance in November 1999 and then expanded in February 2000 to a full-time regular role as an ER nurse and later, after completion of medical school, a Doctor. She was reunited with her former NewsRadio co-star Khandi Alexander, who at that time had a recurring role on ER.
Tierney's highest-profile film while a member of the ER cast was the 2002 film Insomnia, directed by Christopher Nolan. That same year she also starred in Scotland, Pa., portraying a Lady Macbeth-like character written specifically for her by Billy Morrissette, her husband at the time. She was praised by critics for her performance. She also collaborated with NewsRadio Writer Joe Furey for a special "Working with Joe Furey" featurette for Furey's film Love and Support.
In 2004, Tierney won the second-season tournament of Bravo's Celebrity Poker Showdown against Lauren Graham, who had a guest role in the fourth season of NewsRadio. Tierney returned to the stage in May 2006 in an appearance opposite Eric McCormack in the Off Broadway premiere of Some Girl(s). She also appeared in the 2008 films Semi-Pro, Baby Mama, The Go-Getter and Finding Amanda.
Tierney played the role of Laurel in the Off Broadway play Three Changes with Dylan McDermott from September 16 to October 4, 2008.
Tierney had surgery to remove a tumor from her breast in 2009. She had been cast in Parenthood but schedule conflicts with her cancer treatments led her to leave, and she was replaced by Lauren Graham. Tierney finished treatment and returned to work in a stage play in 2010.
Also in 2011, Tierney appeared in one episode of The Office (S8E9: Mrs. California) as Robert California's wife.
In September 2012, Tierney began a recurring role on the CBS legal drama The Good Wife, playing Maddie Hayward.
In 2013, Tierney joined the cast of Showtime's The Affair, playing Helen Solloway. The Affair began airing in October 2014.
