Siddell was born in Auckland and educated at Mt Albert Grammar School and the Auckland College of Education. In 1960 he married artist Sylvia Siddell, with whom he lived in Auckland. They had two daughters, now adults. Siddell had painted full-time since 1972, when he held his first solo show. Following this, he took part in many exhibitions in both public and commercial galleries.
Siddell's realist paintings are identified mainly with depictions of the environs of Auckland. While his works appear to be records of actual places, his paintings have a subjective component, and might be better described as magic realism than truly realistic. The cityscapes and townscapes in Siddell's paintings are rendered empty, but with the unnerving suggestion of events occurring outside the picture area. In this sense, his work can be compared to the metaphysical works of Giorgio de Chirico.
Siddell's work is held in the permanent collections of all New Zealand major public art galleries, as well as many private, corporate and institutional collections. He was appointed a Companion of the Queen's Service Order for community service in the 1991 New Year Honours, and a Distinguished Companion of the New Zealand Order of Merit for services to art in the 2008 New Year Honours. Following the restoration of titular honours by the New Zealand government in 2009, Siddell accepted re-designation as a Knight Companion of the New Zealand Order of Merit. He was only the second New Zealand artist to be knighted, after Sir Toss Woollaston.
In February 2011, a comprehensive survey of his art career was published by Random House New Zealand, "The Art of Peter Siddell."
Siddell died in Auckland on 24 October 2011.
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