The son of an Anstruther merchant family, in 1815 Thomas Chalmers transferred from Kilmeny in Fife to become minister of the Tron parish. When the new parish of St John's was formed in 1819, in the increasingly overcrowded area east of the Trongate, he took responsibility for that and remained there until 1823, after which he moved to become first Professor of Moral Philosophy at St Andrews and then Professor of Divinity at Edinburgh.
It was during his time in Glasgow that he developed his ideas on the maintenance of the poor. He set his face firmly against the idea of poor rate assessed by the local authorities. This would be impersonal and encourage dependency by the poor. Responsibility for the poor, he argued, should remain with the Church and it was important that there should be a personal relationship between the givers of charitable relief and the recipients. This could best be achieved through the small unit of the parish. Through deacons and elders in the church, the poor would be visited and specific help could be directed to each individual in need. They could also get across the message to the poor that self-reliance, self-help and dependence on the family was the solution to their condition. As a powerful preacher he attracted around him many young men who would be influential in Glasgow in the coming years and who actively pursued home missionary activities in the slums.
In theology he was on the evangelical wing of the church and played a very active role in campaigning in the 1830s for an extension of church provision in the cities. He was a key figure in the disruption of the Church of Scotland in 1843, becoming principal of the new Free Church College in Edinburgh in the last four years of his life. He was undoubtedly the minister who was best known outside of Scotland in the 19th century.