He was mayor of Fernie, British Columbia in 1907, but put his political career on hold to serve with the Canadian Army Medical Corps during World War I.

Returning to Halifax, he spent almost a year working as a surgeon at the city's Royal Victoria Hospital before establishing a private practice in Bridgewater, Nova Scotia.

He sold this practice in 1898 and joined the Canadian Pacific Railway Company, which sent him to Coal Creek, British Columbia to work as a surgeon at the local hospital.

[1] While working for the affiliated Crow's Nest Pass Coal Company, Bonnell helped establish the first hospital in Fernie, British Columbia, a city that had been founded in 1898.

[1] He was working in the area on May 22, 1902, the day of one of the worst mining disasters in Canadian history, where 143 miners were asphyxiated after a cave-in near Coal Creek and Fernie.