Ordained a Methodist minister in 1820, Mansfield went to New South Wales as a missionary the same year. Various disputes with the Wesleyan committee in London eventually caused Mansfield to resign as a missionary, but he remained a lay preacher and retained a close involvement with the Methodist church throughout his life. Mansfield became co-editor of the Sydney Gazette
with his friend Robert Howe in January 1829, and on Howe's death shortly afterwards he became sole editor. Mansfield continued the Gazette's traditional policy of supporting the government, taking governor Ralph Darling's side in the controversies over the freedom of the press. After the Gazette's proprietor Ann Howe 'contrived his dismissal' in 1832 (Walker 18), Mansfield wrote for J. D. Lang's Colonist, and from September 1838 he was one of eleven joint owners of that newspaper until it was sold to the proprietors of the Sydney Herald in 1840 (Walker 146). Mansfield's many and varied 'secular' business interests (which included a bookselling business) attracted unfavourable comment from the liberal governor Richard Bourke, as well as his enemies in the liberal press. From 1840, Mansfield became a leader writer for the Tory Herald (from 1842, known as the Sydney Morning Herald). It is generally thought that in the period 1840-1854, Mansfield was in fact the unacknowledged editor of the Herald, and his writing was crucial in shaping the paper's direction in these years (Souter 32-33).
References:
Souter, Gavin. Company of Heralds.
Walker, R. B. The Newspaper Press in New South Wales 1803-1920.
See also ADB.