Flattery joins the consultancy firm from Sage where he was president for Europe and lead a 7000-person business unit across 11 countries. Former roles in his 13 years at Sage included chief executive for UK and Ireland.
Current chief executive Geoff Thompson will become executive chairman as part of proposed board changes announced by the company earlier this year.
Flattery, who will take on the role on 1 October 2016, said: “This is an exciting time in the evolution of the group. Although it has already made significant progress in building out its market leading procurement and energy services businesses, there remains considerable potential to generate further substantial growth across the group.
“I very much look forward to working with the very strong executive team to realise that potential.”
Incoming executive chairman Geoff Thompson commented that he was “delighted” to have secured Flattery to “guide Utilitywise through its next phase of development”.