Singer/actress Demi Lovato is speaking out in favour of marriage equality in a new video for the Human Rights Campaign.

The Skyscraper hitmaker has long supported the fight for gay rights and she recently went public with her personal connection to the cause, revealing her late grandfather was gay.

Now Lovato has signed on as the new face of the Americans for Marriage Equality initiative for the civil rights organisation.

In the 45-second clip, she says, "I believe that love comes in all different shapes, sizes and colours. So whether you're Lgbt (lesbian, gay, bisexual, transgender) or straight, your love is valid, beautiful and an incredible gift...

"Please join me in supporting the majority of Americans who support marriage equality."

Lovato isn't the first celebrity to lend her voice to the Hrc's cause - Bryan Cranston, Julianne Moore, Kristen Bell, Robert De Niro and Neil Patrick Harris have all previously fronted ads to push for the legalisation of same-sex marriage across the U.S.

Gay marriage is currently legal in 19 of America's 50 states.