Martyn was described as "a rabid supporter of Daniel O'Connell" and his repeal movement. In October 1838 he led the men of the parish to a monster meeting at Kiltulla racecourse, where they joined men from the adjoining parishes of Oranmore and Claregalway "in a concerted movement to get relief from the tithes." He led the early efforts against the effects of the Irish Famine but died of typhoid on 24 August 1847 (as had his kinsman, Thomas Barnwall Martin). He is buried in the family vault in Forthill cemetery, Galway.