In December 2013, Mader was cast as the Wicked Witch of the West, a new antagonist for the second half of the third season of Once Upon a Time (in which Mader's fellow Lost star Emilie De Ravin also starred). She also made guest appearances during the second half of season four and was later promoted to a series regular for seasons five and six. In May 2017, Mader announced that she would not be returning for the seventh season of the show, due to a creative decision by the showrunners. However, in September 2017, it was announced that Mader would be reprising her role as Zelena in a recurring capacity for the second half of the seventh season. In all, she made seven appearances in the seventh season, including the series finale "Leaving Storybrooke".