Kristen Carroll Wiig was born on August 22, 1973 in Canandaigua, New York, to Laurie J. (Johnston), an artist, and Jon J. Wiig, a lake marina manager. She is of Norwegian (from her paternal grandfather), Irish, English, and Scottish descent. The family moved to Lancaster, Pennsylvania, before settling in Rochester, New York. When Wiig was 9 years old, her parents divorced and she lived with her mother and older brother Erik.

After graduating from Brighton High School in Rochester, Wiig attended the University of Arizona as an art student. She took her first acting class, as an elective, and was soon encouraged by her teacher to pursue acting. Years later, she moved to Los Angeles and Wiig worked as a main company member of the Los Angeles-based improv and sketch-comedy troupe The Groundlings. As a Groundlings alumna, she joins the ranks of such SNL cast mates as Maya Rudolph, Will Ferrell, Phil Hartman, and Jon Lovitz.

Wiig made her big-screen debut to universal high praise as Katherine Heigl's passive-aggressive boss in Judd Apatow's smash-hit comedy Knocked Up (2007). Additional film credits include Drew Barrymore's directorial debut, Whip It (2009), starring Elliot Page; Greg Mottola's Adventureland (2009), with Ryan Reynolds, Kristen Stewart and Jesse Eisenberg; David Koepp's Ghost Town (2008), with Ricky Gervais; and Jake Kasdan's Walk Hard: The Dewey Cox Story (2007), another Apatow-produced film, in which she starred opposite John C. Reilly. She has also guest-starred on the Emmy-winning NBC series 30 Rock (2006), the HBO series Bored to Death (2009), with Jason Schwartzman, and Flight of the Conchords (2007).

Wiig joined the cast of Saturday Night Live (1975) in 2005, and was known for playing such memorable characters as the excitable Target clerk, Lawrence Welk singer Doonese, the hilarious one-upper Penelope, House Speaker Nancy Pelosi, and Suze Orman, among others. Wiig earned four Emmy nominations for Outstanding Supporting Actress in a Comedy Series for her work on the show. She left the show in the spring of 2012.

In 2011, Wiig co-wrote and starred in Bridesmaids (2011), along with Melissa McCarthy, Maya Rudolph, and Rose Byrne. The film was a box office hit and won several awards, plus earned two Oscar nominations (Best Supporting Actress and Best Original Screenplay), and two Golden Globes nominations (Best Motion Picture - Comedy or Musical and Best Actress).

Wiig also appeared in such notable films as Greg Mottola's Paul (2011), opposite Simon Pegg and Nick Frost; Andrew Jarecki's All Good Things (2010), opposite Ryan Gosling, Kirsten Dunst and Frank Langella; DreamWorks Animation's How to Train Your Dragon (2010), with Gerard Butler and Jay Baruchel; the Universal Pictures' animated feature film Despicable Me (2010), starring Steve Carell and Jason Segel; and Jennifer Westfeldt's Friends with Kids (2011), opposite Jon Hamm, Megan Fox, Adam Scott, Maya Rudolph and Westfeldt.