Whittlesey was educated at Oxford, and owing principally to the fact that he was a nephew of Simon Islip, archbishop of Canterbury, he received numerous ecclesiastical preferments; he held prebends at Lichfield, Chichester and Lincoln, and livings at Ivychurch, Croydon and Cliffe.[1]
Whittlesey was briefly appointed Master of Peterhouse on 10 September 1349 and resigned from that post in 1351.[2] Later he was appointed vicar-general, and then dean of the court of arches by Islip.[1] On 23 October 1360 he became Bishop of Rochester and was consecrated on 6 February 1362.[3] Two years after his consecration he was transferred to the bishopric of Worcester on 6 March 1364.[4] On 11 October 1368 Whittlesey was transferred to the archbishopric of Canterbury in succession to Simon Langham, but his term of office was very uneventful, a circumstance due partly, but not wholly, to his feeble health.[1] He died at Lambeth on the 5th or 6 June 1374.[5]
Fryde, E. B.; Greenway, D. E.; Porter, S.; Roy, I. (1996). Handbook of British Chronology (Third revised ed.). Cambridge: Cambridge University Press. ISBN0-521-56350-X.