Isobar will operate in 19 markets with billings of about $500 million (£273m), 45 per cent of that coming from the online media operations of Carat Interactive. Nigel Morris takes the role of president of isobar.
Morris, a founder member of the Digital Marketing Group in the UK, was named Carat's first global president of interactive business last year. He will report to Aegis CEO Doug Flynn.
The launch will be the fifth network for Aegis, alongside media networks Carat and Vizeum, the outdoor company Posterscope, and market research group Synovate. The group said it was investing in digital because of the rise in online advertising and the rapid development of search and affiliate marketing.
"The creation of isobar provides us with a platform from which to build our digital business. The market for digital services is at a tipping point, with major brands now realising the potential benefits for their business in terms of both brand and response effectiveness," Flynn said.
In a trading statement issued at the same time, Aegis said that March estimates of a 5.3 per cent rise in global ad spend looked conservative.