John Murphy was born in Ireland around 1748. Little is known about his early life but he appears as and engraver in London about 1778, where produced a number of brilliant and masterly mezzotints. His work included portraits and historical and other subjects after contemporary English painters such as Reynolds, Northcote, Romney, Stothard and Benjamin West as well as old masters. He also did work using the stipple method.

He published many of the prints himself; from 1778 to 1788, at No. Air Street in Piccadilly, and afterwards at 18 Warwick Street, Golden Square in London. These were the addresses at which George Keating's father had his bookshops. This assumes some connection between Murphy and fellow engraver Keating (1762-1842) who were both from Dublin.  Murphy was commissioned (along with Richard Earlom) to engrave some of the most important plates from The Houghton Gallery.

After 1788 Murphy was located at 26 Upper Berkeley St. and in 1820 was living in Howland Street, Fitzroy Square. His last known work was done in 1809. His death date is not known.