Later she moved to Chicago and worked with the Piven Theatre Workshop.
Walsh returned to Seattle Grace as a special guest star for episode thirteen in Season 4 and episodes 15 and 16 in Season 5 of Grey's Anatomy.
In 2005, she was cast in her breakout role in the ABC series Grey's Anatomy, as Dr.
Addison Montgomery, the estranged spouse of Derek Shepherd ("Dr. It was announced in February 2007 that Walsh's Grey's Anatomy character would be in a spin-off of Grey's Anatomy that began airing in September 2007.
She sometimes appeared in sketches on Late Night with Conan O'Brien.
She had a recurring role on Karen Sisco as Detective Marley Novak in 20.
Walsh has appeared in several other films with Ferrell, including Bewitched (with Nicole Kidman) and an "alternate film" to Anchorman titled, Wake Up, Ron Burgundy: The Lost Movie. " She played Charlie's mother in The Perks of Being a Wallflower.