The former X Factor judge, 21, is the first celebrity to appear in an ad for HRC's re-launched Americans for Marriage Equality campaign. In the clip, Lovato says she believes "love comes in all different shapes, sizes and colors."
"So whether you're LGBT or straight, your love is valid, beautiful and an incredible gift. ...Please join me in supporting the majority of Americans who support marriage equality."
The "Skyscraper" singer has long been a supporter of the LGBT community and served as the grand marshal of the 44th annual Los Angeles Pride parade in June. She also used the video for her latest single "I Really Don't Care" to advocate for LGBT rights later that month following the revelation that her grandfather was gay.
Same-sex couples are currently allowed to marry in 19 states and the District of Columbia. The HRC said more celebrity endorsements are to come.