Ireland will play Pauline, wife of Frank, who will be played by Tony winner Christian Borle. The couple's story follows them seeking help from Masters in conceiving a child.
William Masters and Virginia Johnson are played by Michael Sheen and Lizzy Caplan. The two are portrayed as pioneers of human sexuality whose research inspired the sexual revolution.
Ireland's work on Broadway includes The Big Knife, After Miss Julie and reasons to be pretty. Her screen credits include "Homeland" and "Mildred Pierce."
Borle's stage credits include Little Me, Peter and the Starcatcher, Legally Blonde, Mary Poppins and Spamalot.
Read Playbill.com's interview with Borle here.
"Masters of Sex" also stars Caitlin Fitzgerald, Teddy Sears and Annaleigh Ashford.
The second season premieres July 13. Visit sho.com/sho/masters-of-sex/home for more information.