Mader was born in 1977 in Cambridge, England. Mader worked as a model in New York City for a year, appearing in adverts for L'Oréal, Colgate and Wella Hair. She began her television career on the ABC daytime soap operas All My Children as Morgan Gordon, and One Life to Live as Margaret Cochran. She also appeared on the soap opera Guiding Light in 2003.
Mader has made number of guest appearances on television shows. In 2006, Mader had a series regular role of the short-lived Fox legal drama, Justice. In 2008, Mader began starring as anthropologist Charlotte Lewis on ABC series Lost. She appeared in the show from 2008 to 2009 and in two episodes in 2010. In 2011 she had a recurring role on No Ordinary Family, and in 2012 made a guest starring appearance on the FOX science-fiction series Fringe, as Jessica Holt. Also in 2012, Mader starred in the short-lived ABC comedy series Work It.
In June 2013, Mader made her stage debut in the role of Barrie in the one-act comedy The Third Date at the Hollywood Fringe Festival. In December 2013, Mader was cast as Zelena, the Wicked Witch of the West, the new antagonist for the second half of the third season of Once Upon a Time. She also made guest appearances during the second half of the fourth season and was later promoted to a series regular for the fifth.
In regards to Mader's personal life, she had once been married to Joseph Arongino, but they announced their separation in 2007. On December 29, 2014, however, she announced her engagement on Twitter to Marcus Kayne.
Gallery of photographic stills used to promote the actor.