His father James was a member of a prominent Corsican family who had migrated to Dublin, Ireland in the early 1730s, where he studied medicine and changed his surname from Matra to Magra.
In 1775, Magra petitioned the King to have his surname revert to its original form Matra, in order to claim a Corsican inheritance.
Matra was the author of the "Proposal for Establishing a Settlement in New South Wales" put forward in 1783, which the immediate forerunner of the official and semi-official "plans" was resulting in the foundation of the first Australian colony.
He looked forward to Australia as an asylum for "those unfortunate loyalists to whom Great Britain was bound by every tie of honour and gratitude and with visions, perhaps, of a reproduction of the life of the planters of Virginia and Carolina".
His biographer, Alan Frost, in 1995, noted that "silence covered Matra's activities until March 1777", when he applied for leave from his post as consul at Teneriffe in the Canary Islands to deal with family matters in British-occupied New York.