On his return in 1896, he studied at Jesus College, Oxford, and obtained a BLitt on Scottish Gaelic dialects.
[1] He married Ella, the daughter of Alexander Carmichael, in Iffley near Oxford in May 1901, just before his ordination as a Church of Scotland minister in June 1901.
[1][2] The most notable works during his tenure were The Norse Influence on Celtic Scotland (1910), and Survivals in Belief among the Celts (1911).
[1] The "Fionn Saga" series he published in the Celtic Review (1904–7) included versions he collected orally from Eriskay, with the assistance of Father Allan MacDonald whom he had befriended earlier.
[3] Henderson contributed some translation work, provided an extensively detailed introduction, and completed the editing of the manuscript for its eventual publication.