McIntyre joins the agency from TKMaxx owner TJX Europe, where he was responsible for establishing a pan-European social media structure and strategy.
McIntyre steps into the role following the departure of Merran Wrigley for an in-house role, and a major restructure of MSLGroup London that was finalised at the end of last year.
He will oversee a team with clients including PFU Fujitsu, Alcatel One Touch and Atos.
His 17-year comms background includes work with clients such as Sony Mobile, PayPal, Intel, Microsoft and Motorola.
It also involved a five-month stint as media adviser for the East Timorean presidential campaign of Jose Ramos-Horta in 2007.
Jeremy Sice, MSLGroup London CEO, commented: "Will's a great guy and brings really interesting experience to the business. The appointment of Will, following the recent senior appointments of Andrew MacDougall and Stanislas Maginant, is a further demonstration of our ambition. It's interesting times here for sure."