Estopinal was elected to Congress upon the death of Adolph Meyer. In the spring of 1919, he died in office, just a few months into his sixth term. His tenure corresponded with the administrations of Theodore Roosevelt, William Howard Taft and Woodrow Wilson. He served on the Naval Affairs Committee. In 1912, he was an alternate delegate to the Democratic National Convention, which met in Baltimore, Maryland, and nominated the successful Woodrow Wilson-Thomas Marshall ticket, a slate which easily prevailed in heavily Democratic Louisiana and nationwide as well. At the convention, Estopinal was a member on the Committee on Rules and Order of Business.