After the First World War, Thomas emigrated to Canada and joined the Alberta Provincial Police in 1921. The force itself was relatively new after having been formed in 1917 to replace the paramilitary Northwest Mounted Police which had just relinquished policing duties in Alberta. He was posted across Alberta throughout his career with the APP was noted as an effective policeman winning the Byron Trophy for being the best shot with a revolver in the entire force. The force was amalgamated with the RCMP in 1932 as a cost-cutting measure during the Great Depression. At the time of the amalgamation, Wallace was an APP Sergeant serving as a drill instructor stationed in Lethbridge. He was allowed retained his rank in the newly formed Alberta detachment of the RCMP after additional training in Regina.
Death and funeral
On 7 October 1935, Wallace had been dispatched with fellow British born RCMP officer Constable George "Scotty" Harrison while in dressed in plain clothed. They were to assist with the capture of three fugitive Doukhobors identified as John Kalmakoff, Joseph Posnikoff, and Peter Woiken. They had been suspected of killing Constable William Wainwright of the Benito police force and RCMP Constable John Shaw. They joined with uniformed RCMP officers G.E Combes and Gray Campbell in an unmarked police vehicle. On 8 October, the perpetrators had robbed a vehicle driven by C.T Scott. Scott had his money and wristwatch stolen by the disoriented fugitives. They bizarrely informed him that they would return his wristwatch if he did not inform the police and continued to follow his vehicle westward as it drove towards Banff. As the two vehicles arrived in Banff, Scott stopped his vehicle before an RCMP checkpoint near the eastern gate of Banff National Park and informed the uniformed Campbell that the men in the vehicle following him had just robbed him. As Wallace and Harrison approached the vehicle, two shots through the windshield were fired by its occupants, hitting both officers. The officers continued to engage the fugitives but had been mortally wounded. Harrison had been shot in the neck, and managed to shoot out the headlights of the vehicle before losing consciousness. Wallace fired his service revolver until he was low on ammunition and collapsed from his wounds. Combes was able to shoot Woiken, killing him instantly while the remaining two perpetrators were tracked down by a combined force of RCMP officers and enraged civilians. Kalmakoff and Posnikoff were both and ultimately shot and morally wounded by civilian William Neish. Wallace was transported to Calgary for medical attention after the shooting where he died of his wounds, with his wife Helen at his side. His partner Harrison also died of his wounds on the same day. At the time of his death, Wallace had been a police officer for 14 years in Alberta. His long years of service were recognized in his massive funeral procession led by the Calgary Highlanders' Pipes and Drums band. He was buried with full masonic and military honours at Calgary's Union Cemetery.
