He taught in Clonmel Technical School from 1903 to 1905, and was later a teacher in Clonakilty Agricultural College. In 1912, he joined the National Health Insurance office as divisional inspector, and after the Treaty was transferred to the Department of Defence, where he was in charge of the dependent’s claim section. A student of the College of Art, he won distinction as an illuminator and sketcher.
Seamus was involved in Irish music from early in his life and even in the turbulent year 1916, Seamus was still extolling the wonders of Irish traditional music. In 1903 the Donegal News reported on 16 May 1903 that Clandillon sang at the second great concert in connection with the Oireachtas. The Freemans Journal in October 1916 informed that the Gaelic League organised its Samhain Festival, and that Seamus Clandillon, the harpist, partook in a concert in the Mansion House. Seamus was a traditional musician often credited with creating the Ceili, which is incorrect – the ensemble simply came to prominence during his period in office.