Her best known roles include Delores Landingham on NBC's The West Wing from 1999 to 2002 and Karen McCluskey on ABC's Desperate Housewives from 2005 to 2012, for which she won two Primetime Emmy Awards in 2005 and 2008.

[1][5] Her first career was as a psychiatric nurse at Michael Reese Hospital in Chicago,[6] living in nearby Lake Forest, Illinois, where she married a psychiatrist and raised two sons.

[7] In 1992, aged 53, she was hired as a street performer working for the Disney-MGM Studios theme park at Walt Disney World in Orlando, Florida.

[8] In 1995, she moved to Hollywood, where she took guest roles in television series such as Roseanne, Home Improvement, Picket Fences, Murphy Brown, ER, Seinfeld, Frasier, Just Shoot Me!, Buffy the Vampire Slayer, Dharma & Greg, Las Vegas and The Drew Carey Show.

In 1999, Joosten took the role of Mrs. Landingham, personal secretary to President Josiah Bartlet (played by Martin Sheen) in The West Wing.

After 2001, she appeared in such shows as Scrubs (appearing in "My Old Lady", which won a Humanitas Prize, as well as reappearing in two later episodes), My Name Is Earl, Spin City, The X-Files, Judging Amy, Monk, Charmed, Will & Grace, Malcolm in the Middle, Grey's Anatomy, The Suite Life of Zack & Cody, Reba, So Little Time, Gilmore Girls, The Closer and a recurring role as one of the less intimidating incarnations of God seen by the title character (played by Amber Tamblyn) on the TV series Joan of Arcadia.

She received Screen Actors Guild Award nominations with the rest of the cast for Outstanding Performance by an Ensemble in a Comedy Series from 2006 to 2008.