He attended President Garfield after he was shot by an assassin on July 2, 1881. This made him the first black physician to attend to a sitting president. Later in 1881 Purvis was appointed by President Chester Arthur as Surgeon-in-Charge at the Freedmen's hospital, serving from October 1, 1881, to 1894. In that role, he was the first black person to head a hospital under civilian authority. In a letter from 1908, Purvis said he believed he was removed by the Secretary of the Interior Hoke Smith in favor of a Democrat after a change in administrations, which was customary for political appoointees.