Samuel Jarvis was educated by the Reverend John Strachan at his Cornwall grammar school and articled with Attorney General William Firth in York in 1810. His education was interrupted by the onset of the War of 1812. He joined Captain Stephen Heward’s flank company in the 3rd York Militia, which served at the capture of Detroit, the Battle of Queenston Heights, Stoney Creek and Lundy’s Lane.
Jarvis was able to secure some minor administrative posts during the War. In 1814 he acted as assistant secretary and registrar to his father, who was the provincial secretary and registrar. Later that year he was made clerk of the Legislative Council to cover the absence of John Powell.
In 1818 Samuel Jarvis married Mary Boyles Powell, daughter of Chief Justice William Dummer Powell. Mary's brother John also served during the War of 1812, and was present at the Battle of Queenston Heights where Isaac Brock and his aide-de-camp John Macdonell were killed. Samuel Jarvis served as a pallbearer for John Macdonell when he was interred with Brock at Fort George. After the war he practiced law in Queenston and Niagara before moving back to York in 1824.