Johnston made her professional stage debut with New York's
Atlantic Theater Company, founded by playwright
David Mamet, where she appeared in many productions including
As You Like It and
Stage Door. She performed with the
Naked Angels Theater Company in
The Stand-In and
Hot Keys, and with
New York Stage and Film in ''Kim's Sister
with David Strathairn and Jane Adams. For her performance in The Lights'' at
Lincoln Center Theater, she was nominated for a
Drama Desk Award for Best Supporting Actress. A
Carsey-Werner casting agent who saw her in
The Lights recommended her for the role of Sally Solomon on the TV series
3rd Rock from the Sun. After numerous auditions in 1996, she won the part, and starred on the show from 1996 to 2001, winning two
Emmy Awards for
Outstanding Supporting Actress in a Comedy Series. She made her feature film debut in
The Debt, winner of Best Short at the 1993
Cannes Film Festival. In 1995, she played Kate in the film
Backfire! She played Esmeralda, a sea hag in
Thrill Ride, a family friendly film released in 2016. Her other television credits include guest-starring roles on
Chicago Hope,
Hearts Afire, and
The 5 Mrs. Buchanans. She narrated
Microscopic Milton on the
Disney Channel. Her significant roles in commercially successful movies include
Austin Powers: The Spy Who Shagged Me in 1999,
The Flintstones in Viva Rock Vegas in 2000,
Music and Lyrics in 2007, and
Bride Wars in 2009. In 1998, she was a spokesmodel for the
Clairol company. Johnston appeared in the sixth and final season of
HBO's
comedy drama series
Sex and the City. In the "
Splat!" episode, her character, Lexi Featherston, an aging party girl, accidentally falls out of a window and dies (after saying, "I'm so bored I could die"), prompting
Carrie Bradshaw (played by
Sarah Jessica Parker) to reexamine her life. In 2005, Johnston was featured in six episodes of
NBC's
ER. In 2009, she was cast as Patsy in a proposed American remake of the British TV series
Absolutely Fabulous. A pilot was filmed but it wasn't picked up to series. She had a recurring role in the 2009 season of
Ugly Betty, and had a single-episode appearance as a
dominatrix in the
second season opener of
Bored to Death. She starred in the
TV Land sitcom The Exes, which ran for four seasons from November 30, 2011 to September 16, 2015. She played divorce attorney Holly Franklin, whose former clients and friends live across the hall in an apartment she owns. Her
memoir, titled
Guts: The Endless Follies and Tiny Triumphs of a Giant Disaster was published on March 12, 2012 by
Gallery Books. The book became a
New York Times best-seller. on the campus of
UCLA. In 2018, she began a recurring role as Tammy Diffendorf on the
CBS sitcom
Mom, and was upgraded to series regular for the show's seventh and eighth seasons (2019–2020). Her character Tammy is Bonnie's (portrayed by
Allison Janney) foster sister and Tammy joins the group's
AA meetings upon being released from prison in season 6. In an interview with
The New York Post, Johnston described Tammy by saying: "She’s probably the dumbest smart person you’ll ever meet. She’s so many things at once. She’s a criminal, but she’s also innocent. She’s clumsy but also very sophisticated. She has no editing button and just says whatever she feels — and it’s usually the wrong thing." In May 2024,
Variety announced that Johnston was cast in
Netflix's
comedy series Leanne alongside
Leanne Morgan. The series was created by Morgan, Susan McMartin and
Chuck Lorre. Johnston plays Carol, who is twice divorced and is loyal to her sister, Leanne. == Public image ==