Rainier was born in England on 24 November 1741, the grandson of Daniel Regnier, a Huguenot refugee who fled France following the revocation of the Edict of Nantes, and the son of merchant Peter Rainier of Sandwich. He enlisted in the Royal Navy in 1756, at the outset of the Seven Years' War. After a period as an ordinary seaman aboard, Rainier was transferred to in 1758. He later served aboard Norfolk, and Burford. On 26 May 1768, working as the master of one of his family's merchant ships, Rainier was promoted to lieutenant. During the AmericanRevolutionary War, Rainier was severely wounded on 8 July 1778, while capturing a large American privateer. He was promoted in rank and went on to become Captain of the 32-gun frigate. He commanded her on the Jamaica Station from 1786 to 1790. In 1790, he became the commander of HMS Monarch. On 8 May 1792, George Vancouver named Mount Rainier in modern-day Washington after Captain Rainier: In early 1793, Rainier commissioned the 74-gun Suffolk. From 1794 to 1805, Rainier commanded Royal Navy operations on the East Indies Station. During his tenure, large swaths of territory came under British control. In 1795, Rainier was promoted to Rear-Admiral. Four years later, he was promoted to the rank of vice admiral. He served in the East Indies as Commodore and commander-in-chief of a fleet. In 1800, he commanded an expedition to Java. On 23 August 1800 Sybille,,, and entered Batavia Roads and captured five Dutch armed vessels in all and destroyed 22 other vessels. The British took one vessel into service and Captain Henry Lidgbird Ball of Daedalus named her, and ordered her manned, armed, and equipped. In 1805 Rainier returned to England and retired from active duty.
Post-military career
After Rainier's retirement, the ministry continued to consult him and in 1805 was promoted to Admiral of the Blue in the celebratory promotions following the British victory at the Battle of Trafalgar. In 1807, he became a Member of Parliament for Sandwich. He died the following year at his home on Great George Street, Westminster. Rainier left an estate valued at £250,000. After having made provision for his near relations, he left ten percent of his estate 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.