"Few persons have a stronger natural talent for [Marine painting] ... than O'Brien and we expect to see him return to his native land an accomplished artist"
Although he is seen as the successor to the Haligonian portraitist William Valentine, John O'Brien is known mainly for his seacapes. Thanks to his attention to detail, his paintings have become valuable documents for historians studying the maritime history of Nova Scotia (The Frank off George's Island, Halifax, c. 1856).
A largely self-taught artist, O'Brien learned by copying American and English engravings and illustrations that he found in newspapers of the time and in Halifax bookstores. In July 1857, he went overseas to study in England. In London, he became a student of John Wilson Carmichael, the British marine painter. He was also inspired by the atmospheric style of Joseph Mallord William Turner, considered the leading British artist of landscapes and seascapes in the nineteenth century.
Upon his return to Halifax nine months later, O'Brien taught painting and had a job colouring photographs for the photographer Wellington Chase. He fashioned himself as an "artist and painter of ornaments" in the city's 1866-67 directory. Aware of the cultural renaissance in Halifax in the 1880s, he returned to easel painting, producing almost half of his known fifty-three works in the studio.