[2] He studied Divinity at Glasgow University graduating MA in 1824 and was licensed by the Presbytery of Hamilton in 1829 and was ordained as a minister by the Church of Scotland at Maxwelltown in Dumfriesshire in 1830.

In 1831 he became assistant to Rev Dr Jones at Lady Glenorchy's Church in Edinburgh,[3] and in 1832 moved to the Middle Parish Church in Paisley[4] before being translated back to Edinburgh to serve Liberton parish in 1835.

[6] Begg was a key figure in the foundation of the Scottish Reformation Society in 1850 and the Protestant Alliance, and was known not only for anti-Roman Catholicism but also his concern for working and living conditions.

Together with Thomas Chalmers, Begg was a major influence behind the colony houses of Edinburgh,[14] which were built between 1850 and 1910 as homes for artisans and skilled working-class families by philanthropic model dwellings companies.

In the late 1850s, alarm at the high illegitimacy rates in the northeast counties led Begg to launch a moral crusade against the accommodation of unmarried male farm servants in bothies.