John Maughan Barnett, born in Leamington, Warwickshire, England, on 21 March 1867, was the son of Maria Gibbs and her husband, John Barnett, a lawyer's clerk. He was educated at a private school and learned the organ from the local parish church organist. He studied piano and composition at the Crystal Palace School, London, and in 1884 was appointed a church organist and choirmaster at Tunbridge Wells. He participated in concerts and gave organ recitals, and in 1889 was appointed organist and choirmaster at the Church of St Mary Magdalen, St Leonards, Sussex. On 4 September that year he married Harriett Frances Tugwell at Tunbridge Wells.
Never robust, Barnett had for several years had a demanding schedule of teaching, composing, organ and piano recitals, as well as a keyboard practice routine of five to seven hours a day. This led to a breakdown of health, and following a farewell recital he and his wife embarked on the Tainui for Tasmania soon after their marriage. Intending to return within 12 months, Barnett was not to see England again for 37 years.
He was appointed organist and choirmaster at Hobart cathedral, also teaching and giving recitals. Wishing to visit New Zealand, he availed himself of an opportunity to tour with the lecturer and humorist Max O'Rell. This decision led to the Barnetts settling in Napier in 1893. Maughan Barnett was appointed cathedral organist and conductor of the Napier Liedertafel.
In 1895 the 'young, enthusiastic, aggressive' Barnett succeeded to the post of organist and choirmaster at St John's Presbyterian Church, Wellington. Over the next 18 years he participated prominently in the diverse musical activities of the city. He soon formed a musical society and, in 1908, became the first city organist. He conducted the Wellington Choral Society in the first New Zealand performance of Elgar's Dream of Gerontius, and was appointed conductor to the society when it amalgamated with the Wellington Musical Union. His very popular organ recitals led to an invitation to inaugurate the new city organ in the Auckland Town Hall in December 1911, and to his appointment in 1912 as Auckland city organist, a position he took up the following year and held until his retirement in 1932. He gave numerous organ recitals to large audiences, conducted municipal choirs, was organist and choirmaster at St Mark's Church, Remuera, and served other musical organisations.
Following Harriett Barnett's death at Auckland in 1925, Maughan Barnett revisited London, presenting organ recitals there and at Leamington. On 22 April 1935 in Auckland he married Mary Duncan Jameson, née Thomson. In the two years prior to his death at Christchurch on 31 July 1938 he served as organist at Christchurch cathedral. He was survived by his second wife and by two of the three daughters of his first marriage, a son having been killed at Gallipoli during the First World War.
Maughan Barnett was an authoritative musician whose keyboard skills were those of a virtuoso. He published A short course of pianoforte technique in London in 1904. Throughout his career he performed frequently as organist, piano soloist, accompanist, and participant in chamber ensembles. During his years as Auckland city organist he played the complete organ works of J. S. Bach in recital. His repertoire included little-known works as well as the principal composers of his day, and many of his own transcriptions. He drew up specifications for the organs at both the Wellington and Auckland town halls and was generous with his knowledge of organ construction. As a choirmaster he had a predilection for unaccompanied works, but his ability as an orchestral conductor enabled him to direct an extended choral repertoire. His energetic participation was a constant stimulus to the musical culture of his adopted cities.
Among his contemporaries, Barnett's compositional technique places him next to Alfred Hill. Several of his choral, vocal and piano works were published in London. Large-scale works include a concert overture, two commemorative odes for soloists, chorus and orchestra, and a piano trio. He also wrote a number of compositions for the interesting combination of carillon and organ. Barnett's most successful works, while seldom innovative in style, demonstrate the instrumental mastery and accomplished musicianship for which all his musical involvement was noted.