Procter himself joined the army as Ensign in the 43rd Foot in April 1781, and served as Lieutenant in New York during the last months of the American War of Independence. His subsequent promotion seems to have been slow, probably indicating a lack of means, as commissions were usually obtained by purchase. Procter married in Ireland in 1792, in which year he became a Captain. Three years later he was promoted to Major. In October 1800 he advanced to Lieutenant Colonel as commander of the 41st Foot. He joined his regiment in Lower Canada in 1802.
Procter remained in command of the regiment, continuously serving in Canada, for ten years. Inspecting officers, including Major General Isaac Brock, commented that his regiment was "very sharp", indicating a good standard of drill and discipline.
Procter won a resounding victory over a brigade commanded by Brigadier-General James Winchester at the Battle of Frenchtown, although his tactics did not escape criticism. Specifically, he allowed his men to open fire too soon, alerting the Americans to his attack. He also placed his artillery well within American rifle range, which resulted in some of the gunners becoming casualties unnecessarily. After the battle, he learned that General Harrison's main army was approaching. Procter had trouble getting enough carts to transport the severely wounded men of his own command, and in his haste to get away, he left 64 severely wounded American prisoners at Frenchtown with only a small guard of Canadian militiamen. The night, some of Procter's liquored-up Indian allies slaughtered every one of the wounded prisoners in what became known as the River Raisin Massacre. This gave American troops a new battle-cry for the War of 1812: "Remember the Raisin!" Nevertheless, Procter was promoted first to Brigadier General and then a few months later to Major General.
In April and May 1813, Procter besieged Harrison at Fort Meigs, Ohio. His artillery pounded the fort for days on end. However, the muddy ground within the fort harmlessly absorbed most of the cannon balls. On May 5, 1813, at the Battle of the Miami Rapids, Procter and the Indians inflicted a devastating defeat on Brigadier-General Green Clay's brigade of Kentucky militia who were trying to reinforce the garrison. A co-operative sortie from the fort by Harrison's command was also severely handled. A large number of American prisoners were taken, and 38 wounded men who had been captured were moved to the disused Fort Miami. There they were massacred by a group of Indians who were frustrated at arriving too late to take part in the battle. Proctor was "involved" or grossly negligent for permitting this massacre to occur. Meanwhile, the Siege of Fort Meigs ended in failure, as did the subsequent Battle of Fort Stephenson.
Following the American naval victory in the Battle of Lake Erie, Procter's supply lines were cut and he was forced to retreat from Detroit. Fort Malden at Amherstburg was also dismantled, since the garrison artillery had been placed on the British fleet for the Battle of Lake Erie and was subsequently lost. The Indian chief Tecumseh reviled Procter for retreating as "a fat animal which slinks away, its tail between its legs". Tecumseh and his warriors nevertheless accompanied Procter's army into Canada.
Procter's retreat was slow and badly organised, and the American army under Harrison caught up with him near Moraviantown. By this time, the British troops were exhausted, demoralized and on half-rations. At the subsequent Battle of the Thames, the British regulars fired their muskets only once before retreating, leaving their Native American allies to fight on alone. Tecumseh was killed and his Indians defeated.
Proctor claimed he had attempted to rally his fleeing troops before galloping off himself, but this was widely disbelieved. He admitted that the conduct of the 41st Foot Regiment, "was not upon this unfortunate occasion, such as I have on every other witnessed with pride and satisfaction ...".
After returning to England in 1815, Procter was effectively semi-retired. He died in 1822 at the age of 59 in Bath.
It has been suggested that his error in judgement at the Battle of the Thames bears a strong correlation with signs of (then undiagnosable) battle fatigue, after his long campaign conducted with insufficient supplies.
Procter's last name is also spelled "Proctor" in many documents and books, though scholars generally prefer "Procter".