Grimaldi was nephew of Thomas Worlidge, to whom in 1764 he was bound apprentice for seven years.
On completing his apprenticeship Grimaldi started life as a miniature-painter, working only in water-colours up to 1785, when he made some essays in enamel painting.
He attracted the notice of Sir Joshua Reynolds, many of whose works, notably his Master Bunbury, Grimaldi copied in miniature; Reynolds recommended him to many persons of distinction, including the Prince of Wales and Prince Frederick, Duke of York and Albany.
He practised in the country as well as in London, but in 1825 settled at 16 Upper Ebury Street, Chelsea, where he died 27 May 1830, and was buried in Bunhill Fields cemetery.
He married, 13 November 1783, Frances, daughter of Louis Barker of Rochester, by whom he was father of Stacey Grimaldi.