The high court will hear a challenge to Proposition 8, a ban on same-sex marriages in California that voters approved in 2008, as well as part of the Defense of Marriage Act, which Congress approved in 1996.
"This is a matter of equal protection under the law," Harris said on CNN. "Same-sex couples should be afforded equal status under the law."
Harris filed a friend of the court brief last month in support of overturning Proposition 8. She also argued that the sponsors of the ban lacked the standing to defend the law in court because they could not prove they were harmed by same-sex marriages.
Harris and her predecessor, current Gov. Jerry Brown, declined to defend the measure in a series of federal court challenges that led to the Supreme Court.
In the nearly five years since Proposition 8 passed by a 52 percent to 48 percent margin, public opinion has shifted in the California and the nation. A Field Poll conducted last month found 61 percent favored gay marriage, while 32 percent opposed it.
Though opponents of gay marriage frequently say that marriage should be limited to one man and one woman in the interest of raising children, supporters say that's precisely why marriage should be extended to gay couples -- for the benefit of their children.
"We have 50,000 children in California right now who are asking, 'why can't my parents be married, too?'" Harris said.