He fast became one of the city's leading contractors, and was responsible for the creation of buildings including the Alberta Hotel and the MacKay Avenue school.

Rather than seek a third term, he challenged incumbent mayor Robert Lee in the 1909 election and finished only forty-nine votes back.

In 1920, Manson left Edmonton to farm in Woodbend, Alberta, where he married M. Rogers, with whom he had a daughter.

On May 10, 1932, Manson and two hired hands set out on a raft down the North Saskatchewan River in search of some missing cattle.

The wind blew the raft into a deep part of the river, where Manson, a non-swimmer, fell out and drowned.