The decision comes after years of discussion, study and outrage over the building of the first full runway in the southeast of the country since World War II. Theresa May's government, reeling from a vote to leave the European Union, was anxious to prove the country was "open for business."
Detractors described it as "catastrophic" for the environment, local community and the owners of 783 homes that are slated to be razed.
"The step that government is taking today is truly momentous," Transport Secretary Chris Grayling said. "After years of discussion and delay this government is taking decisive action to secure the UK's place in the global aviation market."
The government rejected other options to expand airport capacity, including the extension of an existing runway at Heathrow or building a second runway at Gatwick Airport, south of London.
The decision is only the first step, though. The government's recommendation will be studied further and Parliament will vote in about a year. Even if approved, it will take years before construction begins, as residents have threatened to sue to block the project.
Entire communities will be levelled. Compensation and mitigation could cost 2.6 billion pounds ($3.2 billion). But the government said the wider good was at stake.
"This is an important issue for the whole country," Grayling said. "That is why the government's preferred scheme will be subject to full and fair public consultation."
London Mayor Sadiq Khan pledged to explore involvement in "any legal process," as he said Heathrow already exposes the city to more aircraft noise than Paris, Frankfurt, Amsterdam, Munich and Madrid combined. Air quality issues were among Greenpeace's concerns.
But it is the fury of residents that had stalled the project until now. Outraged homeowners argued they had been betrayed by politicians who pledged to block expansion before being put into office - only to change their minds later.
Anti-expansion groups gathered in the village of Harmondsworth, a quintessential English village which traces its history to the 6th century. The third runway is slated to traverse the village, levelling the ivy-covered brick walls of local landmarks like Harmondsworth Hall guest house as well as two thirds of its homes.
"Nowhere else in Europe do they build their runways directly in the heart of residential areas over their cities," said Neil Keveren, who has campaigned against Heathrow expansion for years. The runway grounds would be just across the road from his home, he said.
London and south-eastern England need more airport capacity to meet the growing demands of business travellers and tourists, aviation officials said. Heathrow and rival Gatwick, 30 miles (50 kilometres) south of central London, had offered competing projects that will cost as much as 18.6 billion pounds ($29.1 billion). A furious public relations battle saw placards all over London extolling the virtues of one airport over another.
The issue was so toxic that politicians created an independent commission to weigh the options - and it recommended expanding Heathrow. The commission had already rejected other options, such as one backed by former London Mayor Boris Johnson to build a new airport in the Thames Estuary.
"A new runway at Heathrow is really fantastic news, especially as the country has waited nearly 50 years for this decision," said Paul Drechsler, the president of the Confederation of British Industry. "It will create the air links that will do so much to drive jobs and unlock growth across the U.K., allowing even more of our innovative, ambitious and internationally focused firms, from Bristol to Belfast, to take off and break into new markets."
But in Harmondsworth, the community gathered at the local Five Bells pub to watch the news in disbelief. Some were in tears.
"The fight is only just beginning," said Robert Barnstone, a Stop Heathrow Expansion campaigner. "We will see the government in court and see off this threat - this time for good."