The Playboy founder described the campaign to legalize same sex unions across the US as a "fight for all our rights" in a Politico column.
"Without it, we will turn back the sexual revolution and return to an earlier, puritanical time. Today, in every instance of sexual rights falling under attack, you'll find legislation forced into place by people who practice discrimination disguised as religious freedom," Hefner wrote.
He continued: "[Moral values groups'] goal is to dehumanise everyone's sexuality and reduce us to using sex for the sole purpose of perpetuating our species. To that end, they will criminalise your entire sex life."
Hefner also suggested that denying the LGBT community the right to marry in each state is akin to refusing them human rights.
"No-one should have to subjugate their religious freedom, and no-one should have their personal freedoms infringed. This is America and we must protect the rights of all Americans," he insisted.
Carrie Underwood, Will Smith and US President Barack Obama have also recently come out in support of same sex unions.
Hefner's full column can be read here.