Coughlan was born in Minneapolis, Minnesota. She graduated from Breck School, a small private school in Golden Valley, Minnesota. When she moved to Los Angeles with her father Daniel Merritt Coughlan, she enrolled at the University of Southern California. She studied abroad in Paris in 1995, and graduated with a Bachelor of Arts degree in French in 1996.

Coughlan's first film appearance to gain mainstream attention was in Kevin Williamson's directorial debut Teaching Mrs. Tingle (1999), in which she co-starred alongside Katie Holmes and Helen Mirren. She was cast in the role after reportedly having been rejected for a role on Williamson's series Dawson's Creek. She followed this with a recurring role on the series Wasteland in 1999.

She had a recurring role on the television series Boston Legal as secretary Melissa Hughes in seasons two and three. In 2007, she starred as Jenny McIntyre in Lifetime Television's original series Side Order of Life. Lifetime did not pick the series up for a second season despite a strong following. In 2008-09, she appeared on three episodes of the hit TV show Bones.

Coughlan married Stephen Wallack, whom she had known since they were teenagers in Minneapolis, at a private estate in Pasadena, California on November 1, 2008. They have four children together, Stephen(Finn) Wallack 111, Merritt, Ireland and Connor Wallack. Today, she lives in Deephaven, Minnesota Coughlan resided in Studio City, California until 2015.

Coughlan began writing while she was pregnant and taking time off from acting. She wrote and produced her first pilot, Lost & Found for ABC in 2011. In 2014, she completed writing a comedy based on Peter and Wendy for NBC. In 2016, it was reported by Variety that Fox was developing a comedy series titled Pushing, written by Coughlan and produced by Greg Berlanti.