Scottish nobleman, a leader of the militant Roman Catholic party in Scotland.

Erroll was converted to Roman Catholicism at an early age and succeeded to the earldom in 1585. Between 1588 and 1597 he and his associates were involved in a series of treasonable activities the object of which was the restoration of Roman Catholicism in Scotland, and ultimately in England, by the aid of Spanish money and arms. Twice, in 1589 and 1594, they engaged in armed rebellion, but both rebellions dispersed when King James VI took the field in person. From 1595 to 1596 Erroll was in exile in Holland. On several occasions Erroll and his friends were forced to make a nominal submission to the Reformed Kirk; but in spite of their uniform lack of success and the alarmed hostility of the English government, James VI's determination to preserve a Roman Catholic party as a counterpoise to the ministers of the kirk, and his fear of endangering the English succession by alienating Roman Catholic opinion, prevented any violent retribution overtaking the earls. After 1597 Erroll played little part in public affairs. His religious convictions remained unchanged, and from 1608 to 1611 he was imprisoned as an “obstinate papist.”