Humpherson was elected into the New South Wales Legislative Assembly for the seat of Davidson, at a May 1992 by-election brought on by the resignation of former Education Minister and Liberal-turned-independent member Terry Metherell, who resigned to take up a public service appointment offered by the Greiner government. The Independent Commission Against Corruption undertook an investigation into the appointment amid allegations that this amounted to a corrupt attempt to have Davidson return to the Liberal Party, which had lost its parliamentary majority at the 1991 election. The independents who held the balance of power subsequently forced Greiner's resignation as Premier, but ICAC was found to have exceeded its jurisdiction by the Supreme Court of New South Wales. However Davidson returned to the Liberals, with Humpherson easily winning the by-election ahead of 14 other candidates, despite a 16.1 per cent swing against the Liberal Party. As a backbencher, Humpherson served in various Parliamentary committees, until in 2000 when he was appointed as a Shadow Minister under Opposition Leader Kerry Chikarovski. He held various shadow portfolios including Housing and Corrective Services, Planning and Environment, Justice, Community Services and Emergency Services. Humpherson was narrowly defeated in a preselection battle before the 2007 election in favour of insurance executive, Jonathan O'Dea. Humpherson had cross-factional backing among many delegates, but attracted controversy in local branches after reportedly suggesting party members to quit branches under O'Dea's control, thereby reducing their voting power, a practice known as 'branch stripping'. Despite having support of the Party Leader, Peter Debnam, Humpherson lost the vote 52 votes to 54 and he retired from parliament.
Later career
In March 2007, Humpherson was appointed to the newly created position of general manager of Government and Public Affairs at the Australian Nuclear Science and Technology Organisation and was a member of the management committee. Humpherson left ANSTO in late 2010 to establish his own government relations consultancy, Waratah Advisory, in anticipation of an expected Liberal win at the March 2011 NSW election and accepted a position as Chief of Staff to the newly appointed Resources and Energy Minister, Chris Hartcher.Humpherson then took up a consulting role with the NSW Minerals Council. Since 2015 he has been a Director of Barton Deakin, a Liberal-aligned lobbying firm founded by his former parliamentary colleague, Peter Collins. He became CEO of Barton Deakin in 2019, and currently leads the organisation across it Australian jurisdictions with his deep understanding of politics, extensive senior networks across politics at State and Federal levels and expertise in the resources, energy and development sectors.
