Carey steps into the role having been EMEA and APAC director for Kiip, a network which helps brands reward mobile gamers for in-game achievements.
He will be replacing Pack, who is taking an associate director role at Blue Rubicon in March.
Carey worked as a consultant at Spook Media and Edelman Digital, as well as app-maker Silly Goose and RTE.
Gavin Devine, CEO of MHP Communications, said: ‘His in-depth understanding of the rapidly changing shape of digital communications makes him the ideal candidate to build on and transform MHP’s existing digital capabilities, supporting our ambitious growth plans in 2013.’
Prior to joining MHP, Pack worked as associate director, digital, at Mandate Communications.
He also spent nine years at the Liberal Democrats, running the online campaigns for both the 2001 and 2005 general elections and launching the Lib Dem ‘Innovation Unit.’
Commenting on Pack’s appointment, Blue Rubicon MD Chris Norton said: ‘Mark is one of the UK’s foremost thinkers in online political campaigning. As a true innovator in his field, Mark will enhance Blue Rubicon’s digital leadership, contributing additional campaigning skills to enhance our top class digital team.’