Thomas Ayres was the eldest son of John Ayres, mayor of Hereford, England. The family emigrated to Natal in 1850, but two years later Thomas left for the Australian goldfields. He returned to Natal a few years later and tried to settle as a planter at Cowie's Hill, near Pinetown. However, his main interest was in natural history, particularly ornithology, and from about 1855 he became a regular observer and collector of birds (also to augment his income), and later of insects. At this time he was introduced to the English ornithologist J.H. Gurney* who was on a visit to Natal and the two became lifelong friends. By 1862 Ayres's studies and collecting trips had extended to the borders of the South African Republic (Transvaal). He sold most of his specimens, with field notes, to Gurney, who published the information in a series of ten articles in The Ibis during 1859-1873 under the title "List of a collection of birds from the Colony of Natal in south-eastern Africa". Other specimens were sold to the ornithologists Bowdler Sharpe and Hartlaub. His finds included the type specimens of the new species Zoothera gurneyi (Orange Ground-Thrush) and Promerops gurneyi (Gurney's Sugarbird), the latter described by Jules Verreaux* in 1871. No new local forms at the species level were left to be described in the Durban district after Ayres left Natal. Unfortunately he often did not provice precise localities for his specimens, which limited the value of his work.
In 1865, following the death of his wife, Ayres moved to Potchefstroom to join his brother Jack. They made a living by trading and hunting along the Marico and Crocodile rivers, while Thomas also continued collecting and selling specimens. At some stage he even brewed "Ayre's XX Pale Ale" in Potchefstroom. In the early 1870s he was drawn to the Lydenburg goldfields but had no luck as a digger. At that time he also collected ferns at Mac-Mac, south of Pilgrims Rest. Back in Potchefstroom he was appointed one of the seven members of a committee which was charged with the establishment of a museum in that town. The decision was taken by President T.F. Burgers and his Executive Council in December 1873, without consulting the appointees. They were to form themselves into a "Staats-natuurkundig genootschap" (State Natural Science Association, though usually wrongly named the "State Natural History Association" in English) to promote the study of science (especially geology and mineralogy) in the republic and manage its first museum. The museum did not amount to much and was destroyed during the First Anglo-Boer War of 1880-1881.
In 1880 Ayres accompanied a hunting expedition to Matabeleland (in present Zimbabwe), returning only a year later. His ornithological observations and collections during this trip were later described in The Ibis by Captain G.E. Shelly*. Ayres stayed in Potchefstroom for the rest of his life. His home, known as "The Ark" or "Uncle Tom's Cabin" attracted visitors with an interest in natural history. One of these was the young Austin Roberts*, who spent much time learning from Ayres and later became one of South Africa's best known ornithologists. Another was John Nixon, who described Ayres as "the" ornithologist of the Transvaal. In addition to birds Ayres also collected insects, mainly in the districts of Potchefstroom, Rustenburg and Lydenburg, his most important find being the ants' nest beetle Pausus ayresii. He is recognised for his contributions in this field in the work of L.A. Peringuey*. Roland Trimen*, in the preface to his book South African butterflies... (1887-1889), mentions that the South African Museum acquired a fine collection of Transvaal butterflies from Ayres.
Ayres published a paper on the effects of a snow storm on animal life in the Transvaal in The Zoologist in 1882. However, his main interest remained ornithology and led to the publication of a series of 15 articles under his own name in The Ibis during 1869-1886, with the general title "Notes on the birds of the territory of the Transvaal Republic". Many of the 384 species of Transvaal birds he listed in these articles were observed in the swamps along the Mooi River in the vicinity of Potchefstroom, although he also undertook trips to various other regions of the Transvaal. He is still commemorated in the species names Sarothrura ayresi (White-winged Flufftail), Aquila ayresii (Ayres's Hawk-Eagle) and Cisticola ayresii (Wing-snapping Cisticola). In 1888 he was made an honorary member of the British Ornithologists' Union in recognition of his contributions to the ornithology of South Africa. He was a good field ornithologist and collector, and many of his bird skins ended up in the British, Liverpool, and Norwich museums. His lists of Transvaal and Natal birds served as a point of departure for many later ornithological studies of these regions. As a person he was described as having a sunny nature, being generous and kindhearted, thus winning and keeping friends easily. However, the last years of his life were spent in poor health, partial blindness and poverty. He was survived by a son, Thomas Lambert Ayres, who was a land surveyor in Natal.