National Express agreed to sell its c2c rail franchise to an Italian rival, marking its withdrawal from Britain's railways.
The UK transport group has struck a deal for around £70m with Italy's Trenitalia, part of the industrial conglomerate FS Italiane Group.
It said the sale is conditional on final consent from the Department for Transport, which it expects within a month. The commuter franchise runs out of Fenchurch Street to East London and South Essex to such stations as Leigh-on-Sea and Shoeburyness.
The deal marks the withdrawal of National Express from the UK's main railway network, although it does hold the concession to operate Midland Metro trams between Birmingham and Wolvehampton.
The government took over the group's London-to-Edinburgh East Coast Intercity franchise in 2009 after it was unable to keep up payments on the £1.4bn bid it made to run the key route, due to lower-than expected passenger numbers.
National Express – which operates the UK's iconic coach network – had been the country's largest rail franchise owner, holding contracts to run ScotRail, Midland Mainline and Central Trains.
National Express chief executive Dean Finch said "while not ruling out participating in future UK rail contracts", the group saw significant growth opportunities in the US and across Europe.
Trenitalia said it would retain c2c's existing staff and management, and planned to make further investments in the route.
Trenitalia chief executive Barbara Morgante added: "We see significant chances to invest in UK rail and this in principle agreement with National Express allows us to foster these ambitions."
Trenitalia becomes the latest European operator to be involved in running UK rail franchises, joining Germany's Deutsche Bahn, the Netherlands' Abellio, part of the NS Group, and Keolis, 70% owned by France's SNCF.