Reporting strong financial results today, International Airlines Group has also committed to purchasing up to 42 777X planes from Boeing.
The deal includes 18 orders and 24 options.
The company - which operates British Airways, Iberia and Aer Lingus - joins a group of leading carriers that have selected the new 777-9, which will debut next month as the largest and most efficient twin-engine passenger jet in the world.
The commitment is valued at up to $18.6 billion at list prices.
“The new 777-9 is the world’s most fuel-efficient long-haul aircraft and will bring many benefits to British Airways’ fleet.
“It’s the ideal replacement for the 747 and its size and range will be an excellent fit for the airline’s existing network,” said Willie Walsh, IAG chief executive.
“This aircraft will provide further cost efficiencies and environmental benefits with fuel cost per seat improvements of 30 per cent compared to the 747.
“It also provides an enhanced passenger experience.”
British Airways has been modernising its fleet to more efficiently serve its global route network.
In recent years, the airline has introduced the 787 Dreamliner family to replace its medium-sized widebody jets.
The new 777-9 will replace British Airways’ larger widebody planes, mainly the four-engine 747 jumbo jet.
In ordering the 777-9, British Airways extends a long-running relationship with the popular 777 family.
The airline is one of the largest 777 operators with a fleet of nearly 60 of the long-range jet.
The airline last year committed to four more 777-300ER (Extended Range) jets via operating lease.
The 777X will also debut a redesigned cabin that incorporates popular 787 features and new technologies.
Recently unveiled online, the 777X interior offers larger windows, a wider cabin, new lighting, while providing passengers with a smoother ride, better cabin altitude, humidity, and sound quality.
“British Airways is one of the most iconic international carriers, now in its 100th year of connecting the world with its impressive route network.
“We are honoured that British Airways has selected the 777X as part of its fleet for its next century.
“Together with the 787 Dreamliner, we are excited for the 777X to help British Airways build on its incredible legacy,” said Kevin McAllister, president, Boeing Commercial Airplanes.
“The 777-9, in particular, simply has no competitor in its class when it comes to efficiency and performance.
“It is the right-sized plane for British Airways to efficiently serve long-range routes with heavy passenger demand.”
The selection by IAG and British Airways puts the 777X at 358 orders and commitments from eight customers.
Production of the 777X began in 2017, with first flight planned for this year and first delivery expected in 2020.