At the time of his second marriage to Lucretia Morris on 24 January 1789 at Saint Benet, Gracechurch Street, London, he was described as being of Birmingham.

Watson and his family initially lived at London Charterhouse, where he may have practised as a doctor, but in about 1798 they moved to Hendon, Middlesex.

He was separated from his wife, and by the time of his death in 1824 he was living with his cousin Jane Dickson in Camberwell, London.

He died on 17 September 1824, and his cousin had his body placed in a sealed lead coffin in her parlour.

His cousin was very defensive of him, and recorded that he left manuscripts of unpublished works, including an autobiography, now all lost.