Macintosh was born in Glasgow, where he was first employed as a clerk. He devoted all his spare time to science, particularly chemistry, and before he was twenty resigned his clerkship to take up the manufacture of chemicals. In this he was highly successful, inventing various new processes. His experiments with one of the by-products of tar, naphtha, led to his invention of waterproof fabrics, the essence of his patent being the cementing of two thicknesses of India-rubber together, the India-rubber being made soluble by the action of the naphtha. For his various chemical discoveries he was, in 1823, elected a fellow of the Royal Society.