Francis William Petre, often known as Frank, was born at Petone, New Zealand, on 27 August 1847, the third of 16 children of Henry William Petre and his wife, Mary Anne Ellen Walmsley. His father, one of the founders of Wellington and colonial treasurer of New Munster, was the second son of the 11th Baron Petre, a director of the New Zealand Company. The Petres were one of England's oldest and most influential Catholic families, and Francis's religious faith played a major role in his career.
In 1855 or 1856 Francis returned with his parents to England where he attended the Jesuit institution of Mount St Mary College in Derbyshire from 1856 to 1860. After a brief period at the Royal Naval College, Portsmouth, in 1860–61, he attended Monsignor Haffreingue's college at Boulogne-sur-Mer and completed his education at Ushaw College, Durham. From 1864 to 1869 he was articled to Joseph Samuda of London, a prominent shipbuilder and engineer. He then worked for the architect and engineer Daniel Cubitt Nicholls whose activities ranged from office and warehouse design to sewerage construction. Petre's experience with Samuda and Nicholls provided him with a thorough understanding of the latest engineering techniques including the use of concrete.
In 1872 Petre was employed by John Brogden and Sons as an engineer for railway construction and returned to New Zealand, settling in Dunedin. He supervised the building of the Dunedin to Balclutha and Blenheim to Picton railways before establishing a private engineering and architectural practice in 1875. He continued to practise in Dunedin for the remainder of his career.
On 1 March 1881 at Dunedin, Petre married Margaret Cargill, a daughter of Dorothy and Edward Cargill, prominent members of the Dunedin Presbyterian establishment. This unconventional union, which produced seven daughters and six sons, says much for the independence of mind of Petre and his bride.
Francis Petre's first important architectural commission, St Dominic's Priory in Dunedin, was begun in 1877. This large building, of monolithic concrete construction, was executed in a simplified Gothic style adapted to the innovative use of materials. The success of this work and of the first stage of St Joseph's Cathedral, Dunedin, begun in 1878, established him as the leading Catholic church architect in New Zealand. St Joseph's is a more conventional Gothic design but Petre's engineering skills were needed to overcome the difficulties of its sloping site. He used Gothic for parish churches throughout Otago and Southland, often employing concrete as the principal material as at Sacred Heart Church, North East Valley, Dunedin (1891).
As his practice expanded with the growth of Catholic church building in the 1880s and 1890s Petre received many commissions. The Basilica (later Cathedral) of the Sacred Heart, Wellington (1899), although not his first basilical-plan church, established the pattern for his subsequent large churches in Timaru (1910) and Waimate (1913).
Petre's most important church was the Cathedral of the Blessed Sacrament, Christchurch (1901–5). Based on nineteenth century French prototypes, notably J. I. Hittorff's St Vincent-de-Paul, Paris, the cathedral is constructed of monolithic concrete sheathed in Oamaru stone. Although relations between the architect and the volatile Bishop John Joseph Grimes were often strained during construction, the cathedral is Petre's only major church completed without significant modification to his plans. It reveals both his strength and weakness as a designer: on the exterior the individual elements of the building, especially the dome over the chancel, fail to cohere, but the majestic scale, simplicity and luminosity of the interior are undoubtedly impressive. The largest and most imposing classical church in New Zealand, the cathedral is Petre's finest architectural work.
Petre also designed houses, including Judge H. S. Chapman's Dunedin house (1875), an early example of concrete construction, and commercial buildings in Dunedin and Christchurch. He was active in the establishment of a professional association of architects, being a founding member and secretary of the Dunedin Institute of Civil Engineers and Architects in 1876, a fellow of the New Zealand Institute of Architects on its foundation in 1905, and president of the Institute in 1907–8. He also acted as consular agent for Italy in Dunedin following the death of Edward Cargill in 1903.
A congenial and popular member of his profession, Petre was the first New Zealand-born architect to rise to national prominence. He died at his home in Dunedin on 10 December 1918, survived by his wife, who died in 1933, and all 13 children. A pioneer in the use of concrete in New Zealand architecture, he employed this material more extensively and more imaginatively than any of his contemporaries. Despite Petre's success as an architect his buildings never fully transcended the limitations of his training, although as an engineer, skilled in finding innovative solutions to constructional problems, he led his profession.