Nixon and Marinoni, who have been together since 2004, have one son, Max Ellington Nixon-Marinoni. Nixon also has two children from her previous relationship with photographer Danny Mozes.
Nixon, a 2012 Tony Award nominee for Wit, won the Tony Award in 2006 for her performance in Rabbit Hole and was also nominated for Indiscretions. Her other Broadway credits include The Women, The Last Night of Ballyhoo, Angels in America and The Real Thing, among others.