The action by House Speaker John Boehner, R-Ohio, pits Clement -- a partner in the Atlanta firm King & Spalding, who served as solicitor general under President George W. Bush -- against his predecessor, Theodore Olsen, the Los Angeles Times reported Monday. Olsen joined Democratic lawyer David Boies in a California case that led to a federal judge declaring the law unconstitutional.
The law, enacted in 1996, allows states to withhold recognition from same-sex marriages in other jurisdictions. Five U.S. states, the District of Columbia and a number of foreign countries now allow same-sex couples to marry.
The Obama administration has said it would not defend the law, although it will continue to enforce it until the challenges are settled.
"At last we have a legal eagle on this case who actually wants to win in court! Paul Clement is a genuinely distinguished lawyer, a former solicitor general of the United States, who we are confident will win this case," Brian Brown, president of the National Organization for Marriage, said in a statement. "Thanks to Speaker Boehner's actions, President Obama's attempt to sabotage the legal defense of DOMA is not going to work."