Oliphant fought at the Battle of Dunbar in 1296, where the Scots, under their king John Balliol, were defeated by the invading English.

[b][3] During the siege of 1304, when the castle was attacked by the forces of Edward I of England, the garrison eventually surrendered to the English.

[6] For 110 shillings, as "William Olyfaunt, Knight",[c] he was bonded by Hugh le Despenser, the elder and remained in England until 1313.

[2] He had a safe conduct to return to Scotland on 21 October of that year and was a witness to a charter of King Robert the Bruce in February 1314–15.

These included Dupplin, Hedderwick and Cranshaws which he inherited from his Oliphant predecessors; Aberdalgie, Turin, Glensaugh, Pitkerie and Gallery which apparently came into the family from a Wishart heiress; Gasknes, Newtyle, Kinpurnie, Auchtertyre, Balcrais, Muirhouse and Hazelhead acquired as gifts from the King.