 Mason-Cox would ordinarily have been formally elected to the Legislative Council at the 2007 election, but Forsythe resigned on 13 September 2006. and Mason-Cox was appointed to the resulting casual vacancy and was sworn in as a Member of the Legislative Council on 28 September 2006.Mason-Cox raised the state of infrastructure in the Monaro region and the ongoing battle between New South Wales and the Australian Capital Territory over water rights in the Queanbeyan region as early legislative priorities.Mason-Cox was appointed as the Minister for Fair Trading, in May 2014, but was not appointed to the second Baird ministry following the 2015 state election.