Branch said Tuesday that he filed the paperwork with the Texas Supreme Court opposing a lawsuit that seeks to overturn a ban on gay marriage in Texas.
Texas has a constitutional amendment that defines marriage as between a man and a woman.
But same-sex marriage is currently legal in 13 states and the District of Columbia, and the U.S. Supreme Court recently overturned a federal law preventing gays from receiving the same benefits as other married couples.
Branch, a Republican and currenly a member of the Texas House of Representatives from Dallas, has made opposition to gay marriage a key talking point in his bid to replace Attorney General Greg Abbott.
Branch said he worked with Abbott on the brief.
Abbott is running to replace Gov. Rick Perry.
This material may not be published, broadcast, rewritten, or redistributed.