Lewen will be responsible for leading the agency sales team in generating revenue for Microsoft Advertising, and will work closely with Microsoft's roster of media agency clients.
In his new role, he will report to Chris Maples, commercial director for consumer and online at Microsoft Advertising UK.
Lewen joined Microsoft Advertising as group sales manager in January 2009 and has been responsible for managing agency relationships with Aegis, Havas, IPG and i-level and has led key strategic accounts such as COI, Sky, Orange, Vodafone and BBC.
Prior to joining Microsoft, Lewen spent almost 10 years at outdoor media owner CBS Outdoor, where he worked on the digital division, Alive, and helped drive growth in sectors such as motors, retail and alcohol.
Maples said Lewen's "vision for the agency business, combined with his experience and enthusiasm, meant he really stood out from the crowd" and he would be "hugely successful in adding value as we continue to grow our business and deliver marketing leading service to our customers".
Carolan joined Microsoft in July 2008 and left after just one year to start up his own furniture, art and design company with his brother.
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