He preached in Philadelphia at St. Luke's Episcopal Church and St. Paul's Episcopal Church in the Chestnut Hill neighborhood until 1863, when he moved to Minnesota, hoping the climate change would help his wife's heath. However, he returned to Philadelphia to take a position at the Church of the Ascension, then for three years, Hare served as the general agent of the foreign committee of the board of missions. In 1872 he was elected Missionary Bishop of Niobrara, named after the Niobrara River in Nebraska. In 1883 that diocese was split, and Bp. Hare's part was extended to include the State of South Dakota. He wrote several pamphlets on missionary work in the West.
One of the leading missionaries in America, Hare earned the title "the Apostle of the West" for his dedicated work in the rural Dakotas among pioneers and Native Americans.
Hare died in Atlantic City, New Jersey. His body was returned to South Dakota for burial outside his diocese's cathedral; it was briefly reinterred at the school, and then returned to the cathedral lawn.