After completing his studies, he pursued a practice as an architect in London and married Margaret Anne Jones in 1870 at Newport, Wales.

His London practice was successful, but he suffered from bronchial asthma and received medical advice to leave England.

[2][3] When the Borough of East St Leonards amalgamated to form the Municipality of North Sydney on 29 July 1890, Vernon was an Alderman of the new council, but did not seek re-election when his term expired in February 1891.

[1] On 1 August 1890, Vernon was appointed as the New South Wales Government Architect, however his staff numbers were reduced significantly.

[5] Vernon showed that the system of design competitions were twice as expensive and the activities of this office were boosted in 1894 when extra funding was committed as a way of creating relief work during the Depression of the 1890s.

[8][9] He retired as New South Wales Government Architect in 1911 and returned to private practice, establishing a partnership with Howard Joseland.

[7] In 1911, Vernon judged the competition entries for Parliament House in Wellington, New Zealand, after the original buildings were destroyed in a 1907 fire.