George Cavenagh arrived in Sydney, New South Wales, in 1825. He became a clerk in the Sydney Gazette office in 1833 and from 1 September 1836 to 30 November 1839 was editor of the Gazette (he shared the editorship with Charles Henry Jenkins in January/February 1837). W.C. Wentworth wrote a scathing letter to the Gazette about an item written by Cavenagh, and Cavenagh successfully sued him for libel. Cavenagh moved to Melbourne where in January 1840 he commenced publishing the Port Phillip Herald. He established a job printing office and in 1841 printed the Melbourne Almanac and Port Phillip Directory. He continued his association with the Port Phillip Herald, renamed the Melbourne Morning Herald and General Daily Advertiser, and ultimately the Herald, until 1855.
Various stories circulated in the colonies about Cavenagh and his origins, largely propagated by his enemies and rivals, such as John Dunmore Lang, who alleged in an unpublished pamphlet in 1840 that he was a 'notable swindler' guilty of 'nefarious conduct', and that he had been a drummer-boy, a butler, and a con-man.