He studied medicine at the University of Edinburgh and practised at the Edinburgh Foundling Hospital as a surgeon.
He was sent to the High School in Edinburgh. He translated several scientific works into English, such as Antoine Lavoisier"s work of 1789, Traité Élémentaire de Chimie, published under the title Elements of Chemistry in a New Systematic Order containing All the Modern Discoveries, in 1790. In 1792, he published The Animal Kingdom, the first two volumes of a four-tome translation of Linnaeus" Systema Naturae, which is often cited as the taxonomic authority for a great many species.
(He never did the remaining two volumes) In 1794 he left his post as a surgeon to manage a paper mill.
He lost much of his fortune with this enterprise. Out of economical necessity he began writing again in 1809, publishing a variety of minor works, for instance a General View of the Agriculture of Berwickshire.
His last work was a translation of Cuvier"s Recherches sur les ossements fossiles de quadrupedes, which was published after Kerr"s death under the title "Essays on the Theory of the Earth". His other works included a massive historical study entitled A General History and Collection of Voyages and Travels in eighteen volumes.
Kerr began the series in 1811, dedicating it to Sir Alexander Cochrane, Knight Bachelor, Vice-Admiral of the White.
Publication did not cease following Kerr"s death in 1813. The latter volumes were published into the 1820s. He is buried in Greyfriars Kirkyard in central Edinburgh against the eastern wall.
His stone is added to a much earlier (1610) ornate stone monument.