The original structure was rebuilt in the 15th and 16th centuries, and restored in the 19th. The ornately carved pulpit dates from 1633 and the font possibly from the previous century.
Llywelyn and Joan are depicted in stained glass in the church, in a pair of windows created in the 1930s. Also commemorated here is Evan Evans (1795 to 1855), a bard who was skilled at many styles of poetry and prose. His bardic name was Ieuan Glan Geirionydd, and he grew up on a farm near Trefriw. He first studied at the school in St Mary’s Church, then at the free Llanrwst grammar school. The family fell into poverty when farm rents were raised. Evan became a priest in Cheshire and returned to Trefriw for the last three years of his life. He won chairs at eisteddfodau, edited periodicals, wrote hymns and translated philosophical books. His grave is in the churchyard.
Local historian Morris Jones wrote in 1879 that ministers had neglected the church, where the congregation had dwindled, before the Rev John Gower arrived (in 1869). The rector (pictured left) held services in Welsh and English on Sunday mornings, Sunday school at 2pm and, in the summer, evening sermons in English and Welsh. Hundreds of people from outside Trefriw came to listen, and the church was overfull.