East Midlands, ranked the fourth-largest regional airport in England by passenger numbers, is owned by Derbyshire, Leicestershire and Nottinghamshire county councils and Nottingham City Council.
National Express beat off competition from a management buyout team as well as from Regional Airports, a private company, and the airport operations division of Lockheed.
The airport handled 1.3 million passengers in the year to 31 March and 22,400 tonnes of freight and mail. It mainly serves Derby, Nottingham, Leicester and Sheffield.
It made pre-tax profits of pounds 3.4m in the year to 31 March on turnover of pounds 17.8m, and had net assets of pounds 37.4m.
National Express, the privatised former National Bus Company, was floated on the stock market in December after being bought out by its management in 1988.
It is the dominant coach operator in the country and made pre-tax profits of pounds 6.8m last year. It expects the airport purchase to enhance earnings.
The company is raising pounds 3.75m from the placing of 1.8 million new shares at 210p to partly fund the acquisition.
The rest of the consideration will come from cash balances and a pounds 17.5m seven- year loan from Bank of Scotland.
Adam Mills, finance director, said he believed National Express clinched the deal because it offered the right price and stressed regional development in its talks with the local authorities.
'Our plans are to widen the catchment area of the airport considerably through providing transport links on an economic and reliable basis. Our experience in passenger handling will enable us to funnel people through to the airport effectively.'
Negotiations with tour operators were well advanced. 'We can bring them business economically if they're prepared to route their customers through East Midlands.' National Express shares rose 8p to 223p.Reuse content