John Calcott St Quentin is believed to have arrived in New Zealand from the Australian goldfields about 1863. The date and place of his birth are not known. He had a wife, Sarah Anna Toll, a son, John Alfred Ernest, born probably in 1847 or 1848, and a daughter, Ellen. In 1864 he was a judge of the poultry section of the Canterbury Agricultural and Pastoral Show and organiser of a mounted volunteer corps; in 1868 he helped organise the Anniversary Day sports in Christchurch. In 1865 he made transparencies for a public lantern-slide show to mark the proposed visit to Canterbury of Governor George Grey.
As a supporter of the politician W. S. Moorhouse, St Quentin, already a well-known and popular figure, helped set up the Canterbury Working Men's Association in December 1865. At the inaugural meeting he spoke in support of universal manhood suffrage and education for all, and attacked indirect taxes because they burdened working people. In January 1866 St Quentin was elected secretary of the Canterbury Freehold Land Society, a short-lived project to enable working men to buy small allotments of freehold land. In 1866 he stood unsuccessfully for Papanui on the Canterbury Provincial Council but received a surprisingly large number of votes, 133 to T. S. Duncan's 237. As part of his platform St Quentin was highly critical of the apathy of the administration over major public works projects and denied rumours that he wanted to banish the Bible from Canterbury schools; 'No man in creation had a higher reverence for that best of all books.' Although his fondness for brandy was notorious, St Quentin in July 1867 supported the formation of the Canterbury Alliance, which aimed to control the drinking trade. In January 1868 he stood for the Christchurch Borough Council and in 1869 for the Christchurch City Council, but was narrowly defeated both times.
In June 1868 his design for the borough seal was approved unanimously, with much praise for his artistic taste and knowledge of heraldry. His design combined native birds and plants with sheaves of wheat and an English oak, with a white crane symbolising 'that savage life is giving place to civilisation' in Canterbury. He earned his living as a painter of shopfronts and commercial signs, but also decorated free of charge the chancel walls of the Church of St John the Baptist, Latimer Square. St Quentin's greatest work is undoubtedly the decorated ceiling of B. W. Mountfort's provincial council chamber. According to legend, this work took two years and two barrels of brandy to complete; in fact, it was finished in four months in early 1867, using stencils designed by Mountfort. The red and gold of this richly coloured Gothic Revival ceiling perfectly completed the overall effect. One of the corbels in the council chamber has St Quentin's portrait, carved by his friend William Brassington. St Quentin is described as a tall good-looking man, rather striking in appearance, 'whom one would judge a gentleman'.
In August 1868 St Quentin tried unsuccessfully to establish a public library and school of design in Christchurch. He helped organise the benefit show for R. H. Cox, retiring manager of the Theatre Royal. In 1869 he suffered an unprovoked assault by George Oram at the ball for the Duke of Edinburgh; the magistrate convicted Oram and fined him 20s.
Nothing is known of St Quentin beyond 1869 from Canterbury sources. J. A. E. St Quentin married Mary Ann Emerson in 1870, and after her death married Lucy Brooks in 1898. Ellen St Quentin married W. H. Dawe in 1878.