 After working for the Crown Law Office from 1933 to 1935 he started his own civil law practice in 1936 and was admitted to practice before the High Court of Australia in 1942.Wanstall not only practised in civil law, he practiced broadly including in criminal law.An example of his criminal law practice was when he was called to the represent his old school mate a local Gympie butcher from Gympie, who was charged with cattle rustling (stealing cattle), and such case Wanstall convincingly had his old school mate, acquitted.