Schwarzenegger says the action is consistent with a state Supreme Court ruling upholding the marriages of same-sex couples who tied the knot in California before voters approved Proposition 8.
Proposition 8 is a constitutional amendment passed in November that limits marriage to a man and a woman.
The bill signed by the governor late Sunday also says gay and lesbian couples who were married in other states after Proposition 8's passage have the same rights and benefits that California grants domestic partners.
The bill was sponsored by Democratic Sen. Mark Leno of San Francisco.
