Joosten died Saturday morning from lung cancer, and was surrounded by family and friends at the time of her passing, E! News has confirmed.
She was 72.
"Kathryn passed away this morning after a valiant fight against her cancer," Nadine Jolson, Joosten's rep, told E! News. "Her family was with her. Funeral arrangements are pending. This is a terrible loss, and she fought as hard as she could."
Joosten, who was a fixture on Housewives playing the trouble-causing, gossipy neighbor (she was originally introduced in season one as Lynette Scavo's nemesis), went on to win Emmys in 2005 and 2008 for Outstanding Guest Actress in a Comedy for her role on the show.
Before joining "Housewives," Joosten scored roles on "Dharma and Greg," "My Name is Earl," "Ally McBeal" and more, and was well-known for her role as Mrs. Landingham, the president of the United States' secretary, on "The West Wing."
Joosten, who spent many years working as a psychiatric nurse, kicked off her career as an actor at the age of 42.