His father, William Nelson, was an immigrant to Colonial America from Newsham, North Yorkshire, England.

Along with his younger brother Robert Nelson, he was known as a member of the Patriotes and for his leading role in the Lower Canada Rebellion.

In 1827, he was elected as a member of the Legislative Assembly of Lower Canada, but he gave up active politics in 1830, without disavowing his reformist allegiance.

He became a Patriote leader in the region of the Richelieu River valley, and supported the use of arms at the Assemblée des Six-Comtés in 1837.

In a prelude to the Lower Canada Rebellion of 1837, Nelson led 5,000 Patriotes in the two-day Assembly of the Six Counties in Saint-Charles, Lower Canada (present-day Quebec), on 23 and 24 October 1837, to protest the government's Russell Resolutions, taking place despite the 15 June Proclamation forbidding public assemblies.