After high school he attended McGill College, where he studied natural sciences and civil engineering under the geologists John William Dawson and Thomas Sterry Hunt, graduating with honours in 1860.
[1] While a student Vennor collected Montreal Island fossils and wrote on ornithology for the Canadian Naturalist and Geologist and the British American Magazine of Toronto.
For fifteen years he worked on the geology of Ontario and Pontiac County, Quebec, paying close attention to the Survey's aim of assisting economic development by mining.
[1] At the end of that year, Vennor was visited in Montreal by Mark Twain, who said of him in an after-dinner speech at the Windsor Hotel "Canada has a reputation for magnificent Winter weather, and has a prophet who is bound to deliver it.
[1] Mary Smith Vennor died in November 1920 and was buried at Mount Royal Cemetery, Montreal.