William Hartley (born at Wyn, in Derbyshire, England, of a yeoman family about 1557; executed at Tyburn, 5 October 1588) was an English Roman Catholic priest. He is a Catholic martyr, beatified in 1929.
At eighteen he matriculated at St John's College, Oxford, where he became a chaplain. Being ejected by the vice-chancellor, Tobias Matthew, in 1579, he went to Reims in August, was ordained at Châlons, and returned to England in June 1580.
Hartley helped Robert Parsons and Edmund Campion in printing and distributing their books in England. On 4 August 1581 a search of Stonor Park in Oxfordshire found the press on which Campion's Decem Rationes had been printed. Hartley, along with members of the Stonor family, printers and some servants, were arrested at Stonor Park. Hartley was sent to Marshalsea Prison, London. Here he was detected saying Mass in a cell before Lord Vaux, and for this he was laid in irons on 5 December 1583.
He was indicted for high treason, 7 February 1584, but for some reason, not tried. In January 1585, he was sent into exile. He then spent some little time at Reims, recovering his health, and made a pilgrimage to Rome on 15 April 1586, before returning to the English mission.
In September 1588, he was arrested in Holborn, London, and, as his friend Father Warford said, incurred the suspicion of having apostatized.
Less is known of Hartley's companions.