Percival Henry Hall Thompson was born at Eling, Hampshire, England, on 5 May 1874, the son of Henry Hall Thompson and his wife, Agnes Spooner. After education at a private school he entered the Royal Navy's training ship Britannia as a midshipman in 1887. He was a cadet for two years, then served on various overseas stations, including Australia. On 21 June 1899 he married Helen Sidney Deacon at London; they were to have four children. Sometime after his marriage Thompson became known as Hall-Thompson.
From 1905 Hall-Thompson was based mainly in London. On 30 June 1913 he was promoted to the rank of post captain. His association with New Zealand resulted from the Reform government's decision, in 1913, to begin a locally oriented naval training programme. When approached, the British Admiralty nominated Hall-Thompson to serve as naval adviser and commander of the Philomel, an ageing cruiser which would be the embryo of the New Zealand Naval Forces. The New Zealand cabinet approved his appointment on 7 April 1914 and he began his three-year engagement on 1 May: the first in a succession of British officers to lead the New Zealand Naval Forces over the next 46 years. A handsome man with a genial and breezy personality, Hall-Thompson arrived in New Zealand aboard the Maunganui on 24 June 1914. He was later joined by his wife and children.
As naval adviser in Wellington, Hall-Thompson was immediately immersed in the practical issues involved with implementing the new training programme. He hoisted his pendant as commander of the Philomel on 15 July 1914, and on 30 July took the vessel to Picton on a shakedown cruise. However, at Picton that same day he received news that war with Germany was imminent. He hastily returned to Wellington where the decrepit Philomel was prepared for war service. On 3 August, in accordance with the Naval Defence Act 1913, control of the Philomel was formally transferred to the British Admiralty.
Hall-Thompson left New Zealand with the Philomel on 15 August 1914 on escort duty with the force which occupied German Samoa at the end of that month. Following this successful mission, the Philomel escorted the main body of the New Zealand Expeditionary Force, which left Wellington for the Middle East on 16 October 1914. For the next two years the cruiser was deployed mainly in the Persian Gulf: showing the flag, mediating between Arab tribes and harassing the Turks. Hall-Thompson effectively maintained his aged ship and kept up crew morale in trying conditions.
By early 1917 the minister of defence, James Allen, was impatient to consult Hall-Thompson about naval policy and sought his return. The Philomel, now no longer fit for service, also returned, arriving at Wellington on 16 March 1917. Hall-Thompson later wrote a brief account of the ship's activities for the semi-official history of New Zealand's participation in the First World War. His own services were recognised when he was made a CMG.
Impressed by Hall-Thompson, Allen was keen for him to continue serving as naval adviser after the war. In the meantime he wanted him to gain further operational experience, a course Hall-Thompson also favoured. However, the Admiralty decided he should stay in New Zealand, and this decision was soon justified when in June 1917 the German raider Wolf laid minefields off Cape Farewell and North Cape. Hall-Thompson, after being slow to accept the possibility of mines in New Zealand waters, organised minesweeping operations in 1918. He also prepared several schemes for the development of the New Zealand Naval Forces, which proved valuable when Admiral of the Fleet Lord Jellicoe visited in August 1919 to advise on future naval developments. The Admiralty decided to replace Hall-Thompson shortly before Jellicoe arrived, a move which angered Allen. Hall-Thompson, who had formed a good relationship with Allen and found New Zealand congenial, also resented being 'hustled' out of the country and hoped that he might eventually return.
Arriving back in Britain on 27 September 1919, Hall-Thompson was immediately involved in organising citizen guards during a railway strike. Early in 1920 he assumed command of the battleship Erin, and two years later became an aide-de-camp to George V. Promoted to flag rank in 1923, he was appointed chief of naval staff and first naval member of the Australian Naval Board. Before proceeding to Australia he advised the Australian prime minister at the 1923 Imperial Conference in London. He was made a CB in 1924.
Hall-Thompson returned to Britain in 1926. He subsequently commanded the 3rd Battle Squadron of the Royal Navy's Atlantic Fleet (1927–28) and the Reserve Fleet (1929–30). He retired in 1932 with the rank of admiral and resided at Hythe, Kent, until his death on 6 July 1950. His wife survived him by nine years. Hall-Thompson was significant as the first head of the New Zealand Naval Forces and as the commander of the first New Zealand naval ship to go overseas in wartime.