Orphaned as a child, he emigrated to Montreal in 1782 and purchased a small brewery in 1786. He invested revenue generated by the brewery in a steamship line between Quebec City and Montreal, and built Lower Canada's first distillery in 1821. He also established the Champlain and Saint Lawrence Railroad, the first railway into Canada, and introduced steam power into Montreal industry.
Molson was elected to the legislative assembly from 1816 to 1820, and was made president of the Bank of Montreal in 1826 and appointed to the legislative council in 1832.