The Hays of Liverpool were born in Coldstream where their parents John Hay, joiner, and Sophia Murdoch had married on 26 July 1810. Their elder son, John, was born on 7 July 1811; the second William Hardie, on 7 December 1813; and the much younger James Murdoch on 15 December 1823. Like so many other wrights at the time their father and his brother William, and their father before them, provided architectural drawings when required.
Of the three brothers the eldest, John, was essentially self-taught and had 'indomitable perseverance and energy of purpose. His surviving letters give a vivid picture of his forthright personality. In his brother James's words 'he was educated chiefly as a surveyor in the city of Edinburgh [and] had early imbibed a strong partiality for the classic styles, and so early had be become imbued with a love of architecture, that in 1834 he was employed to design a monument in his native town on the banks of the Tweed, to the memory of Sir Charles Marjoribanks, the member for Berwickshire. Shortly after this he obtained an engagement in Liverpool… Gradually his classic leanings gave way as he watched the progress of the new style [Gothic] and his mind was thrown back on the study of medieval examples'. Less is known of the training of the second brother, William, who commenced practice at 19 St James Square, Edinburgh, in or before 1837 and became one of the architects favoured by the Free Church Building Society after the Disruption of 1843. The much younger James was probably articled to one of his brothers, and may have been sent for experience to Edmund Sharpe at Lancaster as the best informed gothic revival architect in that area as the resemblance between some of their work and that of Sharpe's assistant and partner Edward Graham Paley suggests.
By 1847 or earlier William and James were also based in Liverpool helping with the volume of business in Merseyside and Cumbria, although initially the success of the practice seems to have been almost entirely based on responding to advertisements for architects in provincial northern English and Scottish newspapers as well as the national press. They obtained the commission for the Free Church in Portree directly and won the competition for St John's Anglican Church in Perth, both in 1847; and through the influence of Peter Drummond, the Stirling seedsman, one of the leading lights in the Free Church and the founder of the Stirling Tract Enterprise, they obtained the commission for Stirling North Church in 1852, designed in a distinctly Puginian style. It made their name and their work won the generous praise of James Maclaren in 'The Building Chronicle'. Thereafter their Scottish practice was as much as based on being directly commissioned as on competitions; and although the Stirling church had been of nave-and-aisles form, their early experience as joiners stood them in good stead when they began designing T-plan and oblong wide-span preaching churches with arched laminated principals. The oblong plan churches had a convincing neo-Medieval appearance externally, modelled on Pugin's St Oswald's at Liverpool with its diagonally buttressed tower, but with very original spires. While their success was undoubtedly based on their masterly adaptation of medieval forms, their success with Low Church and Free Church congregations was also fostered by their generous espousal of evangelical and charitable causes: they were 'liberal in theology as well as politics'.
In 1854-55 the Hays built the large towered Greenock Academy without a hitch, but they were less lucky at Stirling where plans approved in 1852 were implemented in 1854, payments to the contractors were allowed to run ahead of actual work, and the contractors declared themselves unable to complete their contract in November 1855. The failure of supervision resulted from chronic over-commitment on widely scattered Scottish sites, the major commission for the new town at Silloth, and a large house in Portugal. It quickly led to the progressive loss of their Scottish practice, their win for the Edinburgh Free Tolbooth Church being cancelled in June 1856 and the commission for St Mary's Free Church, Edinburgh, where the Deacon's Court was particularly difficult, in July 1858. The final professional disaster came in 1860 when the roof of their only classical church, Augustine in Edinburgh began to push out the walls and as at the Free Tolbooth they were superseded by Bryce. The problems there again stemmed from being unable to exercise adequate supervision, James recording that John who dealt almost exclusively with the Scottish practice had been suffering a 'fatal disease', presumably cancer, which had been 'insidiously …operating over his whole system'. John died at Westbury-on-Severn on 3 November 1861, his usual residence being 25 Oxton Road, Birkenhead. The practice itself was based at Delta Chambers, Liverpool. John left a widow and an infant son, William Hardie Hay II, who became a Glasgow-based landscape painter.
Thereafter William and James confined their practice to north-west England undertaking work in Scotland only when directly commissioned. A change of both style and plan is discernible in the practice even before John's death, evidently as a result of the disaster at Augustine: The wide span plans of the 1850s were superseded by galleried plans with cast-iron columns. Their style also changed: although the spires retained their distinctive proportions, their refined late Decorated tracery was replaced by hard Early Geometrical forms.
Although the practice had continued to flourish in Liverpool at a slightly reduced level, it closed after William died at West Kirby on 21 July 1901. James lived on in retirement at Foenum Lodge, Heswall until his death in October 1915. Like his elder brothers he was an outspoken radical to the end, campaigning for peace, prohibition and women's suffrage in the belief that their vote would pave the way to social reform of every description.