Charles James Irwin Grant, 6th Baron de Longueuil, was an Anglo-Canadian nobleman. He was born in Montreal, Lower Canada on 1 April 1815, and was the only male issue of Charles William Grant, 5th Baron de Longueuil and Lady Caroline Coffin. He served in the 79th Regiment as a lieutenant for a while. He later married Henriet Colmore, from whom he fathered two sons (Alexander Frederick, died age 2 and Charles Colmore) as well as a daughter. His wife Henriet died in 1847 and he remarried in Charleston, South Carolina on 18 January 1849 to Anne Trapman, second daughter of Louis Trapman, a consul. He had many children from this union including Reginald Charles and John Charles Moore. He died on 26 February 1879 at age 63.