Sims held the position of chief economics advisor to Prime Minister Bob Hawke,[6] having succeeded Ross Garnaut in this capacity.

[10][11] At the time of his appointment, many competition lawyers expected Sims to take a "tougher" line on anti-competitive conduct than his predecessor.

[12] In 2013 and 2014, Sims' ACCC pushed supermarket companies Coles and Woolworths to limit the size and scope of so-called "shopper dockets" that were seen as undercutting small businesses.

[17][18] Following an agency review of Google and Facebook's impact on local journalism, the ACCC recommended the creation of a News Media Bargaining Code.

[20] In a 2022 interview with The Information, Sims stated that he prefers "pro-competition rules" over proposals to break up so-called Big Tech companies through antitrust enforcement.

[24] Sims is an avid supporter of the Hawthorn Football Club[25] and has stated that he does not use Facebook, but does have a Twitter account "to receive not send".