Joosten, who was also known for playing the president's secretary in the TV series "The West Wing," died Saturday at her Westlake Village home, said her daughter-in-law, Jeremy Joosten.
PHOTOS: Notable deaths of 2012
"This will allow the public to much more comfortably talk about lung cancer," Joosten told the New York Post in February.
The most challenging aspect of the lung-cancer story arc, she said in another interview, was "working with the producers to make sure the material was true and accurate. They have been wonderful about that.
"Secondly, I joke about this being a practice session, but there is a cathartic aspect to it," Joosten said in February on MetroSeeker.com.
Last fall, she called herself a "two-time lung cancer survivor" in a first-person account of the disease that she wrote for The Times.
"My first was in 2001 and my second was in 2009, two completely different lung cancers, one on each side. I am the only 'celebrity' to be public about my lung cancer.
"So far, I am a cancer survivor, but cancer will be with me for the rest of my life, be it as a nodule, tumor or cell someplace, or in my fears and anxieties," she wrote. "Therefore I've decided that I am 'living with cancer.'"
The actress started smoking when she was 16 but quit after her first lung cancer diagnosis, her publicist told The Times in 2009.
On "Housewives" and "The West Wing," Joosten was known for making the most of her sometimes limited scenes, "delivering withering one-liners in her crazy/wise style," The Times said last year.
She had played Karen McCluskey on the hit ABC show since 2005.
Felicity Huffman, one of her "Housewives" costars, wrote Saturday on her Twitter account: "She was an amazing woman and a wonderful actress."
Born Dec. 20, 1939, in Chicago, Joosten did not begin to pursue her "childhood dream" of acting until she was 42.
Previously, she had worked as a psychiatric nurse in a Chicago hospital, where she met and married a psychiatrist. They had two sons, and she embraced life as a suburban housewife in upscale Lake Forest near Chicago.
In 1980 her husband's alcoholism led to a divorce, according to her website, which also says she often supported her family by hanging wallpaper and painting her neighbors' mansions. She would then book many of these same homes for location filming and print ads.
Joosten's mother died in her 40s, and Joosten vowed that she wouldn't have similar regrets at the end of her life.
"She was very angry when she died, because she had literally put off so many things she wanted to do" because of time or money, Joosten said in 2009 in the Oklahoman. "That was a huge lesson for me. I didn't want to get to the end of my life thinking, 'Gosh, if I had only tried…."
So Joosten pursued community theater roles and in 1992 got what she considered her first big break when she spent a year performing at Disney World.
In 1995, she moved to Hollywood "without an agent or connections," she wrote on her website, and five months later got her first part, two lines on the television series "Family Matters."
She landed a recurring role on "Dharma & Greg" and appeared on dozens of other TV shows, including "Ally McBeal," "Scrubs," "My Name Is Earl" and "Joan of Arcadia."
Joosten also appeared in about 20 films, including 2005's "Wedding Crashers" and "Hostage," and "Bedtime Stories" (2008).
She gained more attention for portraying the sharp-tongued executive secretary Mrs. Landingham in "The West Wing," who was killed in a collision with a drunk driver.
When Joosten agreed to appear on "Housewives" she extracted a "verbal promise" from series creator Marc Cherry that "he would not kill me off," she told The Times last year.
"I had just been killed on three different shows. I was tired of it. It was always the big surprise — let's kill Kathryn," said Joosten, who admitted to taking the occasional nap on the couch in her "home" on Wisteria Lane, where she played the meddlesome but lovable neighborhood gossip.
Her "Housewives" cancer story line played a pivotal role in the series finale when the dying Mrs. McCluskey takes the blame for a murder she did not commit.
A year ago, Joosten moved to Westlake Village from Mount Washington and she had recently bought a young horse she hoped to train. She also sat on the board of governors for the Academy of Television Arts and Sciences.
Breaking into the business later in life was a blessing, she once said: "I had it easier because there are literally thousands of beautiful, sexy young twentysomethings trying to get started. I was 55 and able to do comedy. At the time sitcoms were all the rage, and there were plenty of smaller roles for funny old ladies."
Joosten is survived by two sons, Jonathan and Timothy Joosten; two grandsons; and a brother, Henry Jay Rausch.