The UK's highest court gave the go-ahead for the expansion of Heathrow Airport.
The decision allows the £14 billion ($19bn) plan to build a third runway to proceed after decades of legal battles and political wrangling.
The Supreme Court ruled in Heathrow's favour, overturning a previous court decision that blocked the plan on environmental grounds.
On Tuesday, a lawyer involved in the case protested against the court's decision by breaking an embargo to announce the decision himself.
Heathrow, Britain's biggest airport, is keen to proceed despite the plunge in air traffic during the pandemic that led to it losing its crown as the busiest flight centre in Europe.
In February, a court declared the expansion unlawful, with the judge saying that a failure to take into account UK government commitments to climate change was "legally fatal" to the plans.
But the Supreme Court judge told an online session on Wednesday that the government had taken climate change commitments into account when designing its airport policy.
"For these reasons, the court unanimously concludes that the appeal should be allowed. The airport's national policy statement is lawful," Judge Philip Sales said.
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Parking lot: Planes grounded during the pandemic
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Since the ruling against the runway in February, the aviation sector has been hit by its worst downturn, meaning Heathrow now has plenty of spare capacity, but the airport said another runway was still vital for the future.
"Demand for aviation will recover from Covid-19, and the additional capacity at an expanded Heathrow will allow Britain as a sovereign nation to compete for trade and win against our rivals in France and Germany," a Heathrow spokesman said.
The airport is owned by Spain's Ferrovial, the Qatar Investment Authority and China Investment Corp, among others.