During his tenure at O2, Troy contributed to the development of the brand’s 'Be More' advertising campaign, which rolled out last summer.
He will be replaced by Jonathan Earle, who returns to the UK business from his role as chief marketing officer for Telefónica in Slovakia to become head of customer strategy and development.
It comes amid a number of changes in the O2 marketing team. The firm has hired former Paddy Power and Sky marketer Danny Russell to the position of business intelligence business general manager, while Manchester City Football Club chief head of brand Ian Cafferky joins O2 in a newly-created marketing engagement role.
Troy said: "With the launch of the Virgin games brand in the US, it’s an exciting time to join Gamesys.com as it expands globally"
Gamesys was set up by UK-based games developer Noel Hayden in 2001, and launched Jackpotjoy – which has featured Barbara Windsor in its TV ads – the following year.
The Hobbit and Sherlock star Martin Freeman plays a rude wedding guest in Vodafone's first integrated ad campaign since the telecoms giant moved its UK ad business to Ogilvy & Mather earlier this year.