Aselton was born in Milbridge, Maine. She competed in pageants in 1995, and was Miss Maine Teen USA 1995 and first runner-up at Miss Teen USA 1995. She graduated from Narraguagus High School in Harrington in 1996. She attended Boston University School of Communications for two years before moving to Los Angeles to act, where she met her future-husband, Mark Duplass. She then studied for two years at the American Academy of Dramatic Arts in New York.
In 2004, Aselton appeared in a short film titled Scrapple opposite Mark Duplass and his brother Jay Duplass who also wrote and directed the short. Aselton made her feature-length film debut in The Puffy Chair opposite Mark Duplass, who directed the film alongside his brother Jay. The film premiered at Sundance in January 2005 and was released on June 2, 2006, in a limited release. That same year, Aselton appeared opposite Steve Zissis in the short film "The Intervention". In 2009, after a break from acting, Aselton appeared in an episode of The Office. That same year, she appeared in Easier with Practice, "Other People's Parties", and "Feed the Fish". In 2016, Aselton appeared in Togetherness, an HBO original series created by her husband and her brother in law, as Anna. That same year, she was cast in a recurring role in the second season of Casual as Jennifer. Aselton also starred in Fun Mom Dinner opposite Molly Shannon and Toni Collette, directed by Alethea Jones.
Aselton is married to her The League co-star Mark Duplass. They have two daughters together, born in 2007 and 2012.
