johnston returned to boston sometime before 1766. on december 2 of that year he married christy bruce, widow of samuel bruce, becoming stepfather to her two children. he had moved to barbados by 1770, continuing to find work as a portraitist and receiving seventy-five pounds a year to play the organ; a letter from that year to copley makes no mention of his wife or stepchildren, suggesting that they had by this point died. the letter also requests a portrait of his sister, mrs. hobby, from copley. johnston himself died in bridgetown relatively soon thereafter, in april, 1772, apparently of a sudden illness. interment was in the parish church of st. michael. johnston left a will in which his possessions were bequeathed to rachel beckles, sister of barbados attorney general henry beckles. his death was noted in the boston press.