Hugh Fraser Ayson was born in Toiro, near Balclutha, Otago, on 16 November 1884, the son of Lake Falconer Ayson, a rabbit inspector, and his wife, Alice Dabinett. Educated at Masterton School, Wellington College and Victoria College, he was admitted as a barrister and solicitor of the Supreme Court at the age of 21. He became a partner in the Wellington law firm Bunny, Petherick and Ayson in 1905, and on 21 April 1906 at Lower Hutt he married Ivy Ella Hollard. They were to have two children.
In 1916 Hugh Ayson was appointed judge of the Native Land Court and the High Court of the Cook Islands at Rarotonga. In 1922 he became chief judge of both these institutions as well as resident commissioner for the Cook Islands. In addition to serving concurrently in these positions, he held almost all other government powers, including that of appointing, promoting and disciplining government employees. In 1929 he was appointed a CMG for service to the Cook Islands. He remained there until 1937, when he retired to the Native Department in Wellington; but when his successor, S. J. Smith, resigned in 1938, Ayson was reappointed to his former postings.
Ayson was known as 'Judge Ayson' throughout his time in the Cook Islands, even though his main responsibilities after 1922 were administrative. In accordance with the values of the day, the emphasis in administration was more on maintaining the status quo than on developing the region, a policy endorsed by Sir Apirana Ngata, who was minister for the Cook Islands from 1930 to 1934 and to whom Ayson was responsible. For example, even though Ayson was the longest serving resident commissioner, the territory's sole secondary school, which had closed in 1911, was not reopened in his time of service. Little was done to help local institutions to evolve, or to devolve power from his hands other than to reinforce the powers of high chiefs below him.
Ayson is remembered as energetic, thorough and hard-working during the earlier years of his service. Later, as his health deteriorated, he slowed down. Amiable, kindly and considerate, he demanded respect and made his status clear by his demeanour, starched white suit and white pith helmet. A strict dress code was expected of his staff. He had a keen sense of humour, but was intolerant of delay or inefficiency.
Possessing great ability and goodwill, Ayson was nevertheless a man of flawed character. His authoritarian pronouncements are understandable in view of the concentration of power in his hands and the distance from Wellington, but it was doubtless for similar reasons that he abused this power. He was known for the generous supply of liquor he shared with official visitors to the Cook group, even though the consumption of alcohol was illegal in the Cook Islands, except on medical grounds. Some residents disliked him intensely, including those who felt that he favoured chiefs instead of their people in land court decisions – most notably in the case of Makea Tinirau, the high chief of the district of Avarua, who frequently drank and socialised with Ayson. (There was a rival claim to Tinirau's title which was disposed of by the Court.) Several children from Cook Islands mothers are accepted in the community as Ayson's.
In the latter years of his service, Hugh Ayson staggered, his hands shook and his speech was slurred. During court sittings an assistant would stoop beside him, listen to him and then address the court on his behalf. This assistant, according to a popular view, ran the government in his name. Many Cook Islanders believed that Ayson's inability to speak properly resulted from a curse that had been imposed on him after he had made an erroneous decision in the land court. It was also thought that because of staff shortages during the Second World War, he remained longer than would have been ideal. Ill health eventually forced him to leave in December 1943.
Hugh Ayson died at Days Bay, Wellington, on 1 February 1948. His ashes were buried at Avarua, Rarotonga, where a memorial was erected to him. He was survived by the two daughters of his marriage and his wife, Ivy, whose ashes were eventually buried with his.