In 1868, with his growing involvement in New York Republican politics and his relationship with Ulysses Grant from the war, Sharpe became a delegate to the 1868 Republican national convention and campaigned for Grant's nomination for the presidency and then for his election in November. In September 1869, Sharpe was appointed to the Central Committee of the Republican Party of New York and in 1873 he was appointed to the party executive committee. In 1870, President Grant appointed Sharpe United States Marshal for the Southern District of New York as part of Grant's plan to break the Tweed Ring’s hold on the government of New York City. Sharpe oversaw the census that demonstrated that the Democratic victories in the 1868 elections had been due to fraud—a form of ballot box stuffing. He and his marshals also oversaw voter registration and the conduct of elections until Sharpe left the post in 1873.