He was born Julien-Maurice Quesnel in Montreal in 1786, the son of Joseph Quesnel, and studied at the Collège Saint-Raphaël. He joined the North West Company as a clerk and assisted David Thompson in his explorations in 1805 and 1806. He travelled with Simon Fraser on his exploration of the Fraser River in 1808. The Quesnel River, Quesnel Lake and the town of Quesnel, British Columbia were named after him.
In 1811, he returned east and served in the Montreal militia during the War of 1812, reaching the rank of lieutenant. He then moved to Kingston and later York as a merchant, finally settling in Montreal. With a partner, John Spread Baldwin, he became involved in the buying and selling of goods, including the export of timber and flour and owned shares in steamships operating in the region. Quesnel was named a justice of the peace, also served as warden of Trinity House at Montreal from 1830 to 1839 and was a member of the commission for the Montreal harbour. In 1838, he was named to the special council that governed Lower Canada after the Lower Canada Rebellion and, in 1841, he was named to the Legislative Council of the Province of Canada. He died in Montreal in 1842 and was buried in the parish church of Notre Dame.
His brother Frédéric-Auguste was a member of the legislative assembly and legislative council.
Jules-Maurice Quesnel, an advocate married in June, 1816, Marie Josette Cotte, daughter of Gabriel Cotte, and his wife, Angelique Blondeau, who had founded the Catholic Orphan Asylum in Montreal, Quebec. His sisters-in-law were Madame Francois Antoine Larocque and Madame Alexis Laframboise. Jules-Maurice Quesnel died in May, 1842, aged 54. His widow died June 6, 1866.
- "Jules-Maurice Quesnel". Dictionary of Canadian Biography (online ed.). University of Toronto Press. 1979–2005.
- "Biography". Dictionnaire des parlementaires du Québec de 1792 à nos jours (in French). National Assembly of Quebec.
- Morgan, Henry James Types of Canadian women and of women who are or have been connected with Canada : (Toronto, 1903)