Jessup first joined the Grenville Militia in 1829 as an Ensign eventually rising to Captain, and had commanded the Prescott Volunteer Battalion at the Battle of the Windmill in 1838.
Jessup initially served as a junior officer in the Grenville Militia from 1829, eventually becoming a captain, and had led the Prescott Volunteer Battalion at the Battle of the Windmill in 1838.