The couple plan to hold a large reception Sept. 28 outside Seattle where Carlile grew up and will have a third ceremony in her wife Catherine Shepherd's hometown of London in London early next year.
While the decision to marry is personal, it is also political for Carlile and a way for her to stand up for gay marriage.
"It was a crazy feeling when I was filling out the paperwork because I felt like I was breaking a law," Carlile told The Washington Post, "like somebody was going to come in and say, 'You know you can't have this.' It was so exciting. And [Shepherd's] mom and dad were there and it was just really special. So we have a marriage license in Massachusetts."
"It's so surprising," Carlile said, "and so hard fought.... I wouldn't have been able to picture myself married or successful or pursuing my dreams if there hadn't been other people that had done it before me, like role models, and that's why talking about it is so important. If a 14- or 15-year-old girl reads this in a small town who's gay, then she knows that someday she might get to go get a marriage license and get married, and there's no reason she should stop dreaming about a white wedding because I didn't."
The singer's closest friends say Shepherd's presence has changed Carlile in so many ways, and not just personally. It's even reflected in Bear Creek, her latest album released earlier this summer.
Carlile thinks Bear Creek is her best record because of that total freedom. Bandmates Tim and Phil Hanseroth, twins who play guitar and bass for Carlile, think Shepherd made it all possible.
Read more: The Washington Post
See also: Brandi Carlile and Catherine Shepherd Are Engaged