He will now spend six months living and working on Hamilton Island, with the job including a three-bed house and salary of A$150,000 (£74,000).
In return, he has to keep a blog and undertake light caretaking duties, including feeding fish.
The "best job in the world" campaign has been hailed as a huge success for Tourism Queensland in promoting the destination.
It launched in the middle of the northern winter this January, and attracted almost 35,000 applicants and vast amounts of press coverage.
Tourism Queensland boss Anthony Hayes said that an estimated A$110m (£54m) in publicity had been generated by the campaign.
The finalists came from all over the world, including key markets for Australian tourism such as Japan, the US and, of course, Britain.
From 50 shortlisted candidates Tourism Queensland chose 16 finalists, who have spent the past week discovering the taste of Vegemite, snorkelling and taking part in swimming tests in a bid to impress judges.
Winner Southall comes from Hampshire and said that he "loved meeting people" in his video application. He starts the job on July 1.