Kathleen Erin "Kate" Walsh (born October 13, 1967) is an American film and television actress, currently known for her role as Dr. Addison Montgomery on the ABC dramas Grey's Anatomy and Private Practice.

Walsh was born in San Jose, California and grew up in Tucson, Arizona. According to a commercial interview that Walsh did for Cadillac, she explains that her father is Irish and her maternal grandfather came from Italy. Her mother Angela lives in Nevada and Walsh has four older siblings. She has two sisters and two brothers, Sean and Joe, who are film-makers. Walsh studied at University of Arizona for a while where she got involved in regional theatre. She now lives in Los Angeles. Her father came from Navan in Co.Meath, Ireland and he emigrated to America where he met Kate's mother.

Walsh was a model in Japan during the 1980s where she also taught English as a second language to Japanese students. She moved to Chicago and worked with the Piven Theatre Workshop. She performed on National Public Radio in the production of the radio play Born Guilty. Walsh later moved to New York City and joined the comedy troupe Burn Manhattan on June 27, 1987, performing in a number of Off-Broadway plays.