Olson was born in Portland, Oregon. She resided on Vashon Island, Washington, in Puget Sound until the age of eight. Olson later relocated with her family back to the Portland area, to the suburbs of Tigard and Tualatin. Her father, Donald Olson, worked as the publisher of the Portland Tribune. At age 12, Olson was involved in a serious bicycle accident that resulted in a fractured skull, which required reconstructive surgery.
Olson studied theatre at the University of Oregon, graduating with a B.S. in Theater arts in 1997. After college, she moved to Los Angeles to pursue acting professionally.
Olson was a member of the improvisational group the Groundlings. She toured with the USO to Bosnia, Kosovo and Norway. She made several guest appearances in films and television series such as Curb Your Enthusiasm, The Drew Carey Show, The Jamie Kennedy Experiment, Out of Practice, Miss Match, Family Guy, and Punk'd. She had a minor role in the film Coyote Ugly.
In 2004, she was cast as Deandra "Sweet Dee" Reynolds in the FX sitcom It's Always Sunny in Philadelphia. She also voiced Ethel in the first season of the Comedy Central animated series Brickleberry. In the 2013 film The Heat she had a brief but memorable turn as a Bulgarian druggie who engages in an exchange of cultural perspectives and insults with Melissa McCarthy's character.
She played a recurring role as Hartley Underwood, the "one-armed" neighbor in the FX series The Riches. In June 2016, the Human Rights Campaign released a video in tribute to the victims of the 2016 Orlando gay nightclub shooting; in the video, Olson and others told the stories of the people killed there.
Olson stars in a new Fox TV series, The Mick, which premiered in January 2017.
|2000||Eyes to Heaven|
|2000||Coyote Ugly||Bidding Customer|
|2001||Fugly||Cha Cha||Short film|
|2002||Meet the Marks||Kaitlin Marks|
|2010||Held Up||Rocky 2|
|2000–2007||Curb Your Enthusiasm||Becky||6 episodes|
|2002–2004||The Drew Carey Show||Traylor||12 episodes|
|2003||Miss Match||Jillian||Episode: "Who's Sari Now?"|
|2004||Significant Others||Lauren||Episode: "The First Time"|
|2004||George Lopez||Janet||Episode: "Home Sweet Homeschool"|
|2005||Kelsey Grammer Presents: The Sketch Show||Various Characters|
|2005–present||It's Always Sunny in Philadelphia||Deandra Reynolds||123 episodes|
|2006||Out of Practice||Debbie||Episode: "Model Behavior"|
|2007||The Riches||Hartley Underwood||5 episodes|
|2011||Family Guy||Brenda Quagmire|| Voice|
Episode: "Screams of Silence: The Story of Brenda Q"
|2012||Unsupervised||Carol / Danielle|| Voice|
|2014–2015||New Girl||Ashley||2 episodes|
|2015||Bob's Burger||Helen|| Voice|
|2016||Cassius & Clay||Ordwood Cassius||Voice|
Episode: "The Girl Code"
|2017||The Mick||Mackenzie Murphy||Lead Role|