The former American Idol champion, who is a devout Christian, says her own marriage to hockey player Mike Fisher has made her believe all American citizens should be allowed to marry who they want, reported Washington Post.
"I don't know what it's like to be told I can't marry somebody I love, and want to marry... I can't imagine how that must feel. I definitely think we should all have the right to love, and love publicly, the people that we want to love," she said.
Underwood, 29, said that she attends a gay friendly church and does not believe she has the right to judge anyone.
"Above all, God wanted us to love others."
