Born in Shaker Heights, OH, Shannon suffered an unspeakable tragedy early on that turned her world upside down and ultimately fueled her desire to perform. At the age of four, she survived a fatal car accident that killed her mother, Peg, younger sister and cousin, as well as seriously injured her father. Shannon and her older sister, Mary, were unharmed - at least physically. Despite the incalculable loss, her childhood was not a complete tragedy. Not a typical father, Jim Shannon raised his two young daughters alone, and encouraged behavior that would strike fear into the hearts of most parents. He made a point to promote any and all zany antics. When Shannon called her father after she and a friend stowed away on a plane from Ohio to New York City, he was delighted; told her to have a good time and to stow her way back to Ohio when she was done. When it did not work the second time, he happily paid for her and her friend's airfare back to Ohio. Shannon was always performing in front of unsuspecting audiences and her dad was her most ardent supporter; particularly at her Catholic school's annual Saint Patrick's Day pageant. Every year, Shannon eagerly awaited the arrival of Miss Patty and Miss Jackie - choreographers with jet black hair and red lipstick who sported leotards and instructed students through their dance routines. Miss Patty and Miss Jackie left an indelible impression on the budding comic who was being encouraged more and more by her father to push her way out front to center stage. It was all just a rehearsal for bigger things to come.After high school, Shannon studied drama at New York University where she was a classmate of another famous "SNL" goofball, Adam Sandler. Initially enrolled as a drama student, Shannon auditioned for "Follies," a NYU comedy revue. While performing in the show, Shannon realized that she was a natural comedian and it was at that time that she created the character that would help put her on the path to superstardom - Mary Katherine Gallagher. While still attending NYU, she also performed signing telegrams; generally bursting into stag and birthday parties and breaking into a ridiculous song and dance that left her audience bored. However, it was good practice and toughened her up for the difficult career she had chosen. In 1987, shortly after graduating from college, she moved to Los Angeles, joining the ranks of unemployed actors populating the city. After waiting tables for a time, in 1989, she landed the role of Meg in the horror film version of "Phantom of the Opera," starring Robert Englund. Though the roles continued to be infrequent, Shannon managed to land guest spots on David Lynch's "Twin Peaks" (ABC 1990-91), sketch comedy series "In Living Color" (Fox 1990-94) and Ellen DeGeneres sitcom, "Ellen" (ABC 1994-98). But that all changed in 1995 when "SNL" producer Lorne Michaels spotted Shannon performing at a Los Angeles theater in the "Rob & Molly Show," a sketch comedy written by and starring Shannon and her partner, Rob Muir.After joining "SNL" in 1995 as a mid-season replacement for the less-than-popular Janeane Garofalo, whose comedic style did not mesh with the show's, Shannon wasted no time standing out. From the moment she debuted the Mary Katharine Gallagher character, Shannon became a star overnight. Perhaps lesser known, but equally funny in Shannon's repertoire was Sally O'Malley, the unitard-clad former dancer who liked to kick, stretch and boast loudly of being "50 years old!" In fact, O'Malley was oddly inspired by Shannon's father, as well as choreographers Miss Patty and Miss Jackie of her St. Patty's pageant youth. Other standout characterizations included "Goth Talk" public access host Circe Nightshade, quirky joyologist Helen Madden, and NPR radio co-host of "Delicious Dish" (with Ana Gasteyer). Aside from her original characters, the well-rounded Shannon had a knack for imitations as well, including a beret-wearing Monica Lewinsky, an incoherent Elizabeth Taylor and a stoned Courtney Love.Four years after securing her spot as the go-to female cast member on the career-making show, Shannon moved Mary Catherine to the big screen with "Superstar" in 1999. Unfortunately, like most of her "SNL" predecessors who attempted to stretch a five minute skit into a two-hour feature length film, Shannon's first lead role garnered mostly dismal reviews. Nonetheless, Shannon was quickly becoming one of the busiest supporting actress' in some of Hollywood's biggest comedies. In 1997, she stole the show - quite a feat by anyone's standards - as Elaine's (Julia Louis-Dreyfus) coworker, a woman who does not swing her arms when she walks on the "Seinfeld" (NBC, 1989-1998) episode, "The Summer of George." Starting in 1999 until 2004, she landed a recurring role as Val, the unstable, slightly scary neighbor who literally battles Grace Adler (Debra Messing) for the affections of Grace's gay best friend, Will Truman (Eric McCormack), on the NBC sitcom "Will and Grace" (NBC 1998-2006). She then dialed it down a notch playing Kate Beckinsale's sensible best friend in the romantic feature comedy "Serendipity" (2001). Shannon seemed to pop up everywhere that there was need for female comic lunacy, including parts in "Osmosis Jones" (2001), "The Santa Claus 2" (2002), "Little Man" (2006), "Scary Movie 4" (2006), "Talladega Nights: The Ballad of Ricky Bobby" (2006) and "Evan Almighty" (2007). In 2004, Shannon teamed with the equally wacky Mike White - the writer-director behind "Chuck and Buck" (2000) and "The School of Rock" (2003) - in "Cracking Up" (Fox, 2004). In the short-lived sitcom, Shannon starred as a self involved, pill-popping and vodka swilling Beverly Hills housewife. The show was pulled after only a few episodes, but White and Shannon formed a strong friendship, prompting White to promise he would make it up to her by writing a feature script especially for her. In 2007, he delivered the goods with the offbeat dramedy "Year of the Dog," (2006). Not the typical comedic fare audiences were accustomed from Shannon, the film starred the comedian as Peggy, a sweet and unassuming secretary who lives an isolated existence with her beagle, Pencil, whom she loves like a child. When Pencil dies suddenly, Peggy is left adrift with nothing but her overwhelming grief. Shannon delivered a moving and understated performance, winning her some of the best reviews of her career. It was not until after filming began, when one of the dogs in the cast licked Shannon's face and she broke out in hives, that she confessed that she was actually allergic to dogs.In 2007, Shannon returned to television, shooting the pilot for "The Mastersons of Manhattan" (NBC). She also, signed with the Lifetime network to star in a made-for-cable movie "More of Me" (2007) as a stressed-out wife and mother who splits herself into three copies of herself in order to keep up with her hectic schedule. In 2008, Shannon took on the role of Kath opposite Selma Blair as Kim in the American version of Australian sitcom "Kath & Kim" (NBC 2008-09). The series garnered lukewarm reviews and ratings and was canceled after a single season, but Shannon persevered, taking on voice roles in animated hits "Igor" (2009) and "Hotel Transylvania" (2012), as well as animated sitcom "Neighbors From hell" (TBS 2010). Supporting roles in indie comedy-drama "What Goes Up" (2009), broad comedy "Bad Teacher" (2011), telenovela parody "Casa di Mi Padre" (2012) and romantic comedy "The Five Year Engagement" (2012) followed. Shannon maintained a steady presence in the indie film world, co-starring in Clark Gregg's "Trust Me" (2013), Jeff Baena's horror comedy "Life After Beth" (2014), coming of age comedy-drama "Me and Earl and the Dying Girl" (2015) and black comedy "Addicted to Fresno" (2015). After winning a Best Supporting Female Independent Spirit Award for her role in dysfunctional family comedy drama "Other People" (2016), Shannon co-starred in Sarah Jessica Parker's TV comeback "Divorce" (HBO 2016-). She reteamed with director Jeff Baena and star Aubrey Plaza for "The Little Hours" (2017), a quirky comedy set in a 14th century Italian convent.