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. McDreamy", played by Patrick Dempsey). 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. Taye Diggs, Tim Daly, Amy Brenneman, Chris Lowell, and Audra McDonald were cast in the spin-off, "Private Practice". Walsh would return for six episodes across the fourth through eighth seasons of "Grey's Anatomy", including the musical episode "Song Beneath the Song".