Castro has been an advocate for LGBT rights and, as mayor, opposed the law in Texas (later overturned by the U.S. Supreme Court) that denied legal recognition to same-sex marriages. He is also a member of Washington D.C. based think tank the Inter-American Dialogue. Castro was the first San Antonio mayor to serve as the grand marshal of the city's Pride Parade in 2009 and in 2011 led a push to offer domestic partner benefits in the city. In 2012, he joined mayors across the country in signing the "Mayors for the Freedom to Marry" petition for same-sex marriage equality.