He was the grandson of Daniel Regnier, a Huguenot refugee who had fled France following the revocation of the Edict of Nantes, and the son of merchant Peter Rainier and his wife Sarah née Spratt.

In June 1760, he transferred to serve aboard the 64-gun ship of the line HMS Norfolk, which was the flagship of Rear-Admiral Charles Steevens.

In April of the latter year Steevens died and was replaced on board by Vice-Admiral Samuel Cornish, under whom Rainier fought at the Battle of Manila between September and October 1762.

On 8 July of the following year, Rainier engaged and captured a large American privateer, and was badly wounded in the battle.

[1] In Burford Rainier joined the fleet of Vice-Admiral Sir Edward Hughes that sailed for the East Indies Station on 7 March of the same year.

[3] The British took one vessel into service and Captain Henry Lidgbird Ball of Daedalus named her Admiral Rainier, and ordered her manned, armed, and equipped.

He died the following year at his home on Great George Street, Westminster,[1] with his nephew, John Spratt Rainier, succeeding him as MP for Sandwich.

He was not married, and although the bulk of his estate was divided between his nephews, John and Peter Rainier,[1] ten percent was left to the Chancellor of the Exchequer to be used to reduce the national debt, in acknowledgement of: "the national establishment of the Royal Navy, in which I have acquired the principal part of the fortune I now have, which has exceeded my merit and pretensions.

"[5] In 1898 botanist Edward Lee Greene published Rainiera which is a genus of flowering plants in the daisy family, Asteraceae from northwestern United States.