His career, blemished by his suicidal charge at the Battle of Bannockburn, a contributing factor to the devastating English defeat, is perhaps best known for his role in the tale of Sir William Marmion, the chivalric knight of Norham Castle.

[5][non-primary source needed] In May 1303 Grey found himself under the command of Hugh Audley encamped at Melrose Abbey when they were attacked at night by a much larger force led by John Comyn.

[8] A hook thrown from a siege machine ensnared de Beaumont one day, and was about to haul him to his death upon the castle walls, when Grey freed him in the nick of time and dragged him to safety.

[5][non-primary source needed] In December 1307 Grey took custody of Robert Bruce's sister Christina following the execution of her husband Christopher Seton for his part in the murder of John Comyn, Guardian of Scotland.

Grey served under Beaumont and Robert Clifford when they tried to go around the Scottish army on the first day of the battle and met with defeat at the hands of the forces of Sir Thomas Randolph, Earl of Moray.

[18] A two-year truce expired in 1322 and Grey promised the king to recruit an extra 20 men at arms and 50 hobelars to reinforce Lewis de Beaumont's existing garrison to protect both Norham castle and the March.

The king sent Grey money to pay his garrison and requested that he send frequent reports of the situation and reassured the people around the castle that any losses in crops and goods would be made up to them.

[9][non-primary source needed] Edward II agreed to a 13-year truce with Bruce in May 1323 and, three months later, Grey was given permission to go to Scotland to resupply Norham Castle with corn and ammunition and to replace its ploughs and carts which had been destroyed in the preceding years.

[15][non-primary source needed] Grey was ordered to "compel" ships from Northumberland ports to join the fleet and to supervise their departure for Orwell, Suffolk in early September.

[20][non-primary source needed] No naval conflict occurred and, landing at Orwell on 24 September, Isabella and Mortimer seized control of England with virtually no opposition, with most of Edward's orders having been ignored.