John Hill was the second son of the Rev. Theophilous Hill, and was born either at Spalding or at Peterborough in the year 1716 or 1717. Nothing appears to be known regarding his early education; according to Hawkins[59] he did not receive an academical education, but there is no doubt that, as was usual for those who desired to practise medicine at that and at much later times, he served his apprenticeship to an apothecary, it is said, at Westminster; also he attended the lectures on Botany given under the auspices of the Apothecaries' Company at the Chelsea Physic Garden. He first practised in St Martin's Lane in a shop which, according to Woodward[60], was little more than a shed; from there he moved to Westminster, and it appears that at the age of twenty-one he had a practice in Covent Garden. He early experienced financial difficulties; indeed, it is stated that, at times, he was unable to provide himself with the bare necessities of life. His marriage with a dowerless maiden, Miss Travers, did not improve his prospects, and he sought to add to his income by the utilization of his botanical knowledge. He travelled over the country collecting plants, which he dried, put up into sets with descriptions and sold by subscription; also he arranged the collections and gardens of the Duke of Richmond and Lord Petrie. Hill soon found that Botany, from the monetary point of view, was unprofitable; he therefore decided to try his fortune on the stage, and appeared at the Haymarket and Covent Garden.
Woodward[61] gives a very amusing account of him in his new profession. After giving examples to shew Hill's limitations, he remarks: "There was a time at the celebrated Theatre of _May Fair_ he [Marr] represented _Altamont_, and the _Great Inspector_ [Hill] attempted _Lothario_; and the polite Audience of that Place all choruss'd and agreed with you, when you dying, said, 'O Altamont! thy Genius is the stronger.'... Can I forget, great Sir, your acting _Constant_, in the _Provok'd Wife_, and your _innocent_ Rape of Mrs Woffington; when, in a certain Passage, where, at least, a seeming Manliness was necessary, you handled her so awkwardly, that she joined the Audience in laughing at you."