Harold Mitchell has sold Mitchell Communication Group (ASX: MCU), which he founded 34 years ago, to British media company Aegis Group for $363 million. The Australian media mogul will, however, continue to lead the expanded company.

The new firm, which will cover media buying, research and digital marketing, will have an approximated 25 percent of the media buying market in Australia and will build on Mr Mitchell's vision to gain a greater footing in Asia.

The agreement will make Mr Mitchell and his son Stuart the second largest shareholders in Aegis after the 68-year-old media legend has opted to receive shares, instead of cash, in the London Stock Exchange-listed company, consenting to not sell the majority of the stock for two years. He will also assume the role of executive chairman of Aegis Media's operations in Australia and New Zealand.

The deal will give Aegis a larger share of the Australian market and Mr Mitchell the machinery to expand in Asian.

''We didn't really have an Asia platform ... which is where a lot of our clients are so we are really going to be able to build there,'' said Mr Mitchell.

''We will be the biggest. We have not sold out. We have backed ourselves to the hilt.''

Under the agreement, MCU shareholders can opt to receive $1.20 a share in cash, a 15 per cent premium on the last traded price of $1.04, or take scrip in Aegis. The Mitchell family has about 40 per cent stake in the Australian media group.