During the Ilinden–Preobrazhenie Uprising of 1903, Tatarchev guided the revolutionary fight, as the emigrant representation turned out to be the sole governing body of the organization. To his credit, Tatarchev did not desert the revolutionary campaign when the uprising was quelled. Later he came in conflict with the supporters of Yane Sandanski and did not participate in the activities of the IMRO to the Kyustendil Congress in March 1908, where he was appointed as an adviser to the Foreign Committee of the IMRO. After the Young Turk Revolution he openly supported the Union of the Bulgarian Constitutional Clubs, but did not participate in its activities. In 1910 he was elected a reserve member of the Central Committee of IMRO. When Bulgaria entered the Balkan Wars and the First World War, Tatarchev was sent to the front as a regimental physician. At the end of the wars he was one of the initiators of the Temporary representation of the former IMARO.