Apparently it takes a (former) Wallaby to catch a wallaby.

About 5am on Tuesday, a wallaby decided to hop over the Sydney Harbour Bridge, travelling south before taking the Cahill Expressway towards the Conservatorium.

Also on the Harbour Bridge on Tuesday morning was former Wallabies captain Nick Farr-Jones, who decided to help out.

"The police were trying to capture it as you would on the bridge, and they were having trouble so I just did my best to help them," he told 2GB.