Born in Perthshire, Scotland, the son of Adam Fergusson and his first wife Jemima Johnston Blair, he emigrated to Upper Canada with his family in 1833.

He resigned from the bench to run as a Reform Party candidate in the general election of 1847.

He was elected to the Legislative Assembly of the Province of Canada for the riding of Waterloo and reelected in 1851.

Following Canadian Confederation, he was appointed to the Senate of Canada on 23 October 1867 by a royal proclamation of Queen Victoria.

Sitting as a Liberal, he represented the senatorial division of Ontario until his death, only two months and six days after his appointment.