In an opinion column in the Washington Post, Clinton talks about the Defense of Marriage Act, a bill he signed into law in 1996.
Clinton is asking for the Supreme Court to find the law unconstitutional, saying it was a stop-gap to prevent a constitutional amendment banning gay marriage.
Clinton wrote, "I have come to believe that DOMA is contrary to those principles and, in fact, incompatible with our constitution. Reading those words today, I know now that, even worse than providing an excuse for discrimination, the law is itself discriminatory. It should be overturned."
The Supreme Court will hear arguments on a constitutional challenge to the bill at the end of March.