Born in Yorkshire, he made his profession as a Benedictine monk in the monastery of St. Laurence at Dieulward in Lorraine in 1610, and pursued his studies in St. Gregory's monastery at Douai. Subsequently he was sent on the English mission, and he was in prison in Yorkshire, as a Catholic priest, on 1 April 1618. On his release he was employed in reforming the monastery of St. Peter at Ghent.
He graduated D.D. probably at Douai, and acted as secretary to the president of his order from 1621 to 1629. Sent to Germany to negotiate the transfer of monasteries from the Bursfelde Congregation, he was for half a year superior of the monastery of Rinteln, and was subsequently president-general of his order from 1635 to 1641. At the ninth general chapter held in 1643 he was declared the first abbot of Lamspringe.
He died at Hildesheim on 17 March 1651. His remains were taken to Lamspringe in 1692, and buried in the church there.
Reyner was editor of the historical work Apostolatus Benedictinorum in Anglia, sive Disceptatio Historica de Antiquitate Ordinis Congregationisque Monachorum Nigrorum S. Benedicti in regno Angliæ, Douay, 1626. The materials for this work were collected by David Baker, and then his friend, John Jones, alias Leander à S. Martino, wrote up the materials into respectable latinity. In the dedication to Cardinal Bentivoglio, Reyner disclaimed authorship.
- "Reyner, Clement". Dictionary of National Biography. London: Smith, Elder & Co. 1885–1900.
- Augustine Baker, ed. Clement Reyner, Apostolatus Benedictinorum in Anglia (Laurentius Kellamus, Douai 1626). (Bayerische StaatsBibliothek digital) (in Latin)