John Baker was born in the Upper Canada to Dorinda Baker, who was a slave owned by an United Empire Loyalist. The Act to Prevent the further Introduction of Slaves and to limit the Term of Contracts for Servitude established that individuals, like Baker, who were born by mothers who were slaves, were entitled to be freed when they turned 25. However, the will of his second owner, the son of his original owner, freed Baker and the rest of his family, and left them land and funds to support themselves. So Baker became free in 1804 when his owner died during a shipwreck. Baker's brother Simon died in the same wreck.
At some point prior to The War of 1812, Baker enlisted in a Nova Scotia based regiment when it was stationed in York, Upper Canada. During the War of 1812, he fought in Sackets Harbor, New York, the Battle of Chippawa, the Battle of Lundy's Lane, and the siege of Fort Erie. After Peace was declared, he transferred to another regiment that served in Europe and fought in the Battle of Waterloo.
Baker returned to Canada, married, and worked as a general labourer.
Baker lived a long life, and when a newspaper reporter interviewed him in 1868, he was believed to be the last surviving individual who had been born a slave, in Canada. He died in 1871.