The son of a Scarborough builder, Thomas Postgate, by his wife Jane Wade, he was born in Scarborough, on 21 October 1820. He started his career as a grocer's boy at the age of eleven.Postgate (2001), pp. 7-13 but, shocked by such practices as adding sand to sugar and plaster of Paris to flour, he apprenticed himself to two Scarborough doctors. He had taught himself chemistry and botany and went on to become a licensed apothecary in London where he discovered that drugs could often be dangerously impure. He attended lectures at the Leeds school of medicine.
