He earned the nickname "The Green Hornet", after the comic book and radio serial character of the same name, because he "always knew what the bad guys were doing" during his turn as orderly officer.
Promoted major in August 1944, he was severely wounded at Hoogerheide in October, but returned to the battalion in 1945 to see the end of the war.
After the war Tennant served as the Training Officer of the Calgary Highlanders, now a Militia unit again, and in 1948, he became Second in Command of the Regiment.
On July 13, 1977, he was appointed Honorary Lieutenant Colonel of The Calgary Highlanders, remaining in that position into 1981.
His Order of Canada citation reads: For many years of service to his community, not only as Honorary Lieutenant-Colonel of the Calgary Highlanders but as alderman and active member of the boards of many organizations including the Canadian Institute for the Blind, the Hospital Board, the City Transportation Commission and the Calgary Centennial Committee.On the fiftieth anniversary of Holland's liberation in May 1995, the City of Doetinchem named a park "Mark Tennant Plantsoen - A Canadian Liberator".