One of the premier Unitarian hymn writers. Hosmer was born in Framingham, Massachusetts on October 16, 1840, the son of Charles and Susan Hosmer. He graduated from Harvard College in 1862, and then went on to Harvard Divinity School. Here he became friends with William Channing Gannett, with whom he would later collaborate to produce hymnals. When he finished Divinity School in 1869 he was ordained in the fall at the church in Northborough, Massachusetts, where he remained as pastor for three years. This was followed by a ministry in Quincy, Illinois. He then went on to a very successful ministry at the First Unitarian Church of Cleveland, Ohio from 1878-92. It was during this time that he began to work on hymns in earnest.
In 1880 Hosmer collaborated with Gannett and James Vila Blake to produce Unity Hymns and Chorals. Then in 1886 he and Gannett produced The Thought of God in Hymns and Poems. His hymns began to find their way into other hymnals especially after 1900. Thirty-five of his hymns appear in Hymns of the Spirit (1937). From 1894-1899 Hosmer served the Church of the Unity in St. Louis, Missouri. His final ministry was at the First Unitarian Church of Berkeley, California from 1900-1915. While he was minister in Berkeley, he wrote the popular “Forward Through the Ages” (set to the tune St. Gertrude) for the dedication of the Oakland church. He also delivered a series of lectures at Harvard Divinity School on hymnody. In Berkeley he was made emeritus, and he remained there until his death on June 7, 1929. The author of eight hymns in the current Unitarian Universalist Association (UUA) hymnal, Singing the Living Tradition, his reputation as a hymn writer rivals that of Samuel Longfellow in Unitarian history.