John Courtenay (c. 1435 – May 4, 1471) was a son of Thomas de Courtenay, 13th Earl of Devon and Margaret Beaufort, Countess of Devon.
He was the younger brother of Thomas Courtenay, 6th Earl of Devon. He married Laura Bourchier although they have no known descendants. It was his brother who knighted him on 29 December 1460 after the Battle of Wakefield. After Battle of Mortimer's Cross, Edward, Earl of March marched and took the capital from the Lancastrians. Parliament voted an attainder on his opposition, and John declared a traitor. the new King Edward IV marched north and sealed his reign with the bloody victory on Towton Field.
At the readeption of Henry VI on 9 October 1470, John was restored to ancestral lands by the Lancastrians. The Yorkists marched south in alliance with Earl of Warwick and defeated the governing house at Battle of Barnet, just outside London on 14 April 1471. The decisive Yorkist victory ended Henry VI's brief return to power and all nobility, including John Courtenay were deprived of their possessions, titles and honours. Still unmarried he died May 4, 1471 in the Battle of Tewkesbury.
The effect of the attainder was to terminate the Barony of Okehampton (creation 1299), so that the earldom inherited from Reviers family, was in abeyance, passing laterally to the descendants of his sisters.