Grimes received a Bachelor of Economics from Flinders University in 1989, later completing a Masters of Economics and a PhD in Economics at the Australian National University. His PhD thesis, which he completed in 1994, was titled The Determinants of Trade Union Membership: Evidence from Two Australian Surveys. He finished his secondary education at the Armand Hammer United World College of the American West in 1984. In the SouthAustralian public service, Grimes obtained the role of Deputy Under Secretary in the Department of Treasury and Finance. Between March 2005 and January 2007, Grimes was ACT Under Treasurer in the ACT Public Service. In the role he oversaw the ACT Government's transition to the GFS accounting system, a change that then Treasurer Jon Stanhope suggested would enable the Government to have a more realistic and less volatile basis upon which to base budgeting decisions. He also assisted in developing and delivering the 2006–07 ACT Government Budget, which involved major structural change to ACT Government agencies; and consolidated IT and procurement services across the ACT public service. In January 2007, Grimes took up an Australian Public Service position as Deputy Secretary in the Department of Finance and Administration. He stayed in the Department when it transitioned to become the Department of Finance and Deregulation, heading the Budget Group as its General Manager. Grimes was appointed Acting Secretary of the Department of Sustainability, Environment, Water, Population and Communities in September 2010, moving into the role formally in 2011. His responsibilities at the Department included matters related to environment protection and conservation of biodiversity, air quality, national fuel quality standards and administration of the Australian Antarctic Territory. In September 2013, after the Abbott Government was sworn in, Grimes was transferred to head the Department of Agriculture. In the role, Grimes was responsible for matters including the agricultural, pastoral, fishing, food and forest industries, rural adjustment and drought issues, food security policy and programs, and quarantine. In March 2015, Agriculture Minister Barnaby Joyce announced Grimes would be stepping down from his Secretary position, with media reporting that Joyce and Grimes were understood to have different philosophical views on environmental issues. Grimes reportedly wrote that he "agreed that the minister would be better supported... by a new secretary with a different background and set of policy skills." Grimes was appointed Commissioner of the Victorian Public Sector Commission in December 2017. His term begins on 22 January 2018.
