Henry was born on May 2, 1915, in Chauvin, Alberta. He enlisted at No. 13 District Depot as a General Reinforcement in October 1943 in Calgary. After training in Ontario, he embarked for the United Kingdom on June 25, 1944, arriving on July 3, 1944. He was taken on strength by the 1 Armoured Personnel Carrier Regiment, Canadian Armoured Corps, Canadian Active Service Force, on November 12, 1944.
Trooper Johnston was declared killed in action on January 17, 1945, during an attack in which his Regiment was carrying members of the Devonshire Regiment, a regiment of the British Army, as part of Operation BLACKCOCK. He was buried as an unknown soldier in 1945 in Mook War Cemetery, the Netherlands, his name commemorated on the Groesbeek Memorial to the Missing.
Research received in 2018 suggested Henry's grave had been identified at Mook and this was subsequently confirmed by the Canadian Casualty Identification Review Board in late 2019.
The rededication service at Mook War Cemetery was attended by family members, Canadian Defence staff, Regimental representatives, CWGC staff and local dignitaries.The CWGC has marked his grave with a newly engraved Commission headstone and will care for it in perpetuity.