A member of the Haida First Nation, Kelly was educated at Coqualeetza Institute and Columbia College, studying theology at both Methodist institutions. Before becoming a lay preacher, he taught school for five years at Skidegate. By 1911 he had begun to distinguish himself as an advocate for Indigenous rights in the discussions surrounding BC land claims and in 1927, as president of the Allied Tribes of BC, he testified on Indigenous grievances before a special parliamentary committee. Kelly believed in assimilation, according to biographer J. H. van den Brink, and supported government abolition of the potlatch. Prominent in the Native Brotherhood of BC in the 1930s, he was a key figure in the consultations of the late 1940s that led to a revision of the Indian Act. As an ordained minister, he also served in several pastorates and as captain of the Thomas Crosby III and Thomas Crosby IV mission ships.
In 1948, Kelly received an honorary degree in theology from the University of British Columbia. In 1957, he was elected president of the Conference of the United Church in British Columbia.