The communications firm has acquired 75 per cent of the company and has an option to buy the remaining 25 per cent it does not own from 2016.
Aegis paid an initial £27m, which gives consideration for MediaVest’s working capital, while the full amount of up to £95m will be paid subject to the firm achieving profit targets between this year and 2016.
Managing partners in the Manchester-based company, Andy Jeal and Dave Lucas, sold their 77 per cent stake to Aegis.
Founded 17 years ago, MediaVest has operations in Manchester, Leeds, Newcastle and Edinburgh and employs 216 staff.
It counts Holland and Barrett, the health store chain, and travel firm Thomas Cook among its clients.
Profit before tax at MediaVest for the year ended 28 February 2011 was £7.4m.
MediaVest will become part of Aegis Media’s Carat and iProspect networks and will immediately start acting under the marketing firm’s brand names.
Aegis chief Jerry Buhlmann said: “[This acquisition] improves our market share in the UK and further increasing our performance marketing and digital capabilities.”
Aegis is currently in the process of selling off its Synovate market research unit. The firm is said to have snubbed an approach from private equity house Doughty Hanson’s corporate adviser, Wyvern Partners.
The Mayfair-based boutique said that it had approached Aegis in advance of the company agreeing to enter exclusive talks with French group Ipsos.