Ann Griffiths (née Thomas) (April 1776 – August 1805) was a Welsh poet and writer of Methodist Christian hymns.
Ann was born in April 1776 near the village of Llanfihangel-yng-Ngwynfa, six miles from the market town of Llanfyllin (in the former county of Montgomeryshire) in Powys. She was the daughter of John Evan Thomas, a tenant farmer and churchwarden, and his wife, Jane. She had two older sisters, an older brother, John, and a younger brother, Edward. Her parents' house, Dolwar Fechan, was an isolated farm-house some two-and-a-half miles south of Llanfihangel and one mile north of Dolanog, set among hills and streams. Not far away lay Pennant Melangell, where Saint Melangell had lived as a hermit in the 8th century.
Ann was brought up in the Anglican Church; but in 1794, when she was eighteen, her mother died, and about this time or perhaps earlier she followed her brothers John and Edward in becoming drawn to the Methodist movement. In 1796 she joined the Calvinistic Methodist movement after hearing the preaching of Rev. Benjamin Jones of Pwllheli.
After the deaths of both her parents she married Thomas Griffiths, a farmer from the parish of Meifod and an elder of the Calvinistic Methodist church.
She died following childbirth aged 29, and was buried on 12 August 1805 at Llanfihangel-yng-Ngwynfa.
She left behind a handful of stanzas in the Welsh language. These were preserved and published by her mentor, the Calvinistic Methodist minister, John Hughes of Pontrobert, and his wife, Ruth, who had been maid at Ann Griffiths' farm and was a close confidante.
Together with Mary Jones (1784–1864), a poor Welsh girl who walked to Bala to buy a bible, she became a national icon by the end of the nineteenth century, and was a significant figure in Welsh nonconformism.
Ann's poems are an expression of her fervent evangelical Christian faith, and reflect her incisive intellect and thorough scriptural knowledge. She is the most prominent female hymn-writer in Welsh. Her work is regarded as a highlight of Welsh literature, and her longest poem was described by the dramatist and literary critic, Saunders Lewis, as 'one of the majestic songs in the religious poetry of Europe'.