Sir John Fenwick, 1st Baronet (c. 1570 – c. 1658) was an English landowner and politician who sat in the House of Commons at various times between 1624 and 1648. He supported the Parliamentary cause in the Civil War.
Fenwick was the son of Sir William Fenwick, who had been Sheriff of Northumberland in 1578 and 1589, and his first wife Grace Forster daughter of Sir John Forster of Edderstone and Hexham. He was knighted at Royston on 18 January 1605. He succeeded his father on 1618 at the age of 35. Fenwick himself also served as Sheriff in 1620. In 1624 and again in 1625, 1626 and 1628 Fenwick was elected Member of Parliament for Northumberland. He was created 1st Baronet Fenwick of Fenwick, on 9 June 1628. He was a successful racehorse breeder and became a favourite of Charles I for whom he acted as Master of the Royal Stud at Tutbury and Surveyor of the Royal Race (or Stud).
In April 1640, Fenwick was again elected MP for Northumberland to the Short Parliament. He was elected MP for Cockermouth to the Long Parliament in 1641 and then re-elected for Northumberland in 1642 after Henry Percy was excluded. Fenwick was temporarily disabled from sitting in January 1644. His son and heir John was killed fighting on the Royalist side at the Battle of Marston Moor in 1644 Fenwick again served as Sheriff of Northumberland in 1645, and was re-admitted to Parliament in June 1646.