After leaving university, Newhouse joined JPMorgan in Sydney as a corporate finance executive and was later transferred to JPMorgan's New York office. From New York he moved to London where he worked for two years as a capital markets lawyer for Clifford Chance. In 1990 he returned to Sydney and continued working as a lawyer with Swaab & Associates. He became an accredited mediator and was a member of the Consumer Trader Tenancy Tribunal from 1999 to 2007 and a mediator for the Workers Compensation Commission from 2001 to 2010.