Luton Airport, which lies 30 miles (50 kilometres) north of central London, is run under a concession held by TBI, owned 90 percent by Abertis and 10 percent by Spain's public airport operator, AENA.
Under the agreement, TBI is to be sold to a consortium held 51-percent by AENA and 49 percent by AXA Private Equity, Abertis said in a statement.
The deal had an "enterprise value" of €502 million , it said.
Enterprise value is a term used to explain the price paid for a business plus other factors taken into account such as debt.
The sale of the London-Luton airport concession, which Abertis had controlled since 2005, formed part of a strategy by Abertis of withdrawing from its worldwide airport holdings.
On July 22, Abertis said it had agreed to sell Belfast International Airport in Northern Ireland and Sweden's Stockholm Skavsta Airport to US operator ADC & HAS Airports Worldwide for 284 million euros in cash.
With the latest deal, Abertis' remaining airport business is limited to a stake in Grupo Aeropuertuario del Pacifico in Mexico and the concession for Montego Bay airport in Jamaica, both of which are for sale.
Abertis said the sale of Luton airport was still subject to clearance by the competition authorities, Luton Borough Concil and the Spanish board of ministers.
Luton airport would have contributed about €141 million to Abertis' group revenue and 46 million euros to group earnings before interest, taxes, depreciation and amortization in 2013, the company estimated.