[2] John Dunmore Lang brought Petrie, his wife and four sons to Sydney in 1831 with other Scottish mechanics (tradespeople) to form the nucleus of a force of free workers to construct the Australian College, which was located in Jamison Street in The Rocks.

[2] He also made inspections of government owned sheep and cattle and placed a number of beacons on navigational hazards in the Brisbane River.

In the new surroundings he was able to pursue two main interests: as builder and architect he was responsible for most of the important structures that arose; and he made many more journeys.

He was the first European to climb Mount Beerwah, one of the Glass House Mountains seen by James Cook, and he was also the first to bring back samples of the Bunya pine.

[6] In 1842 with a small party in a boat he discovered the Mary River and brought back to the settlement two 'wild white men', James Davis or 'Duramboi' and David Bracewell or 'Wandi'.

[3] Such was his courage that he still kept control over his business: when plans were explained to him he ordered the necessary quantities of material and was even able to check the performance of his building workers; he used his cane if not satisfied.

[2] Petrie's work as an architect, stonemason and builder is reflected in a number of public buildings in Brisbane, in particular Newstead House.