Since 2006, Regan has appeared in various television shows and in films. In 2008, she began filming Legend of the Seeker, a television show based on Terry Goodkind's Sword of Truth series. She portrayed Mother Confessor Kahlan Amnell, which earned her a cult following. In 2009, she ventured into producing with Camp Wanatachi, a musical that ran in New York at La MaMa Experimental Theatre Club.
Regan was cast as a lead for the proposed television series The Frontier in 2012. In 2013, she began a recurring role in the fifth season of the USA Network crime drama White Collar as Rebecca Lowe/Rachel Turner. That same year, she joined the series Beauty & the Beast for a multi-episode arc as Alex. In 2014, Regan was cast in a recurring role in Jane the Virgin, as Rose, a former lawyer who is involved in a complicated same-sex love affair. Also in 2014, she had a small role in John Wick, as Addy.
In 2014, Regan was cast in the recurring role of Dottie for 2015 in the comic book-based television series Agent Carter. In 2016 Regan was added to the cast of the TNT drama series The Last Ship for the show's third season, playing the role of Sasha, a current diplomat in Asia and a former Navy Intelligence Officer.