Stelter will head up the strategy team and drive initiatives to increase campaign integration and reduce client costs. He will be based in the agency's London office.
Stelter has over a decade of experience in the search marketing sector. He was formerly director of business development for Texas-based Range Online Media.
Stelter said: "The internet marketing business is rapidly maturing. As the sector continues to develop, clients will increasingly demand greater integration between the various strands of their digital campaigns, not to mention even greater return on their investment, and agencies must be ready to meet the greater challenge.
"They will need a blend of industry-leading technique and international perspective that very few companies actually offer, and I believe Bigmouthmedia is perfectly positioned to provide it."
In addition to experience with agency campaigns across the travel, government, health care and retail sectors, Stelter managed various site and product developments at BizRate.com (now Shopzilla) for over four years and has been a representative on various IAB committees and the DoubleClick Client Advisory Board.
Lyndsay Menzies, managing director of bigmouthmedia UK, said: "In the current economic climate, the focus is on getting clients more bang for their buck, and by leveraging [Stelter's] experience of cross-channel strategies we expect him to lead integrated digital campaigns that deliver even greater levels of ROI.
"As the digital marketing sector's nature becomes increasingly international Phil's experience in the US will also be telling.
"He is a well-known industry figure in America and will spearhead the expansion of our activities there."