As a young man he farmed on the White Horse Plains, led a gold exploration party to Edmonton and then became the first post master for the Hudson's Bay Company at Fort Victoria, Alberta.

[6] In September 1862 Flett wrote from Edmonton that some young men were earning $4 to $5 per day with the rocker, and an old American miner expected to get $10 when he had a sluice built.

[7] In May 1863, Flett wrote that after overwintering the party had reached "Mud Fort" about 55 miles (89 km) above Edmonton the previous month, and were finding gold in the river beds worth between 6s and 10s each day.

[1] Flett and John Norris led the first brigade of Red River ox-carts from Winnipeg to Edmonton, taking three and a half months on the journey.

While at Victoria, Flett made friends with both Methodist and Roman Catholic missionaries, and helped them understand the customs and the language of the Cree.

At first the local Cree were unwilling to grant permission for the mission, which they felt would attract European settlers and drive away the buffalo, but Flett managed to persuade them to accept the missionaries' right to settle there, pointing out that both he and his wife had native relatives.

He was appointed a delegate in the provisional government of Louis Riel, and was involved in debates over the terms on which Red River should join Canada.

[1] At a convention of English and French Delegates in Council at Fort Garry in 1870 Flett said: "For my part, I am a half-breed, but far be it for me to press any land claim I may have against the poor Indian of the country.

[11] In June 1874 Flett was appointed a Presbyterian missionary for a large territory from Fort Pelly to south of Riding Mountain, 150 miles (240 km) away.

The mission, which he called "Okanese" (meaning "Little Bone" in the Ojibwa language), was at the Riding Mountain House Hudson's Bay Company post, near the present town of Elphinstone.

[12] In November 1878 Flett wrote the first of a series of letters to the Canadian Woman's Foreign Missionary Society (WFMS) in Toronto, drawing their attention to the work being done in native Indian missions.