Rachel Reeves has backed a third runway at Heather Airport as part of a fresh plan to boost the UK's economy.
In a speech to business leaders, the chancellor said the expansion would "make Britain the world's best connected place to do business."
The project - which has been delayed for decades over environmental concerns - would inject some optimism into the economy which has flatlined in recent months.
However, the boss of Ryanair has said a third runway at Heathrow will not be ready until 2050, throwing Ms Reeves's plan into doubt. Michael O'Leary warned that the project would face years of delays.
Sir Sadiq Khan also cast his doubts about the announcement, saying: "I'm simply not convinced that you can have hundreds of thousands of additional flights at Heathrow every year without a hugely damaging impact on our environment."
In her speech, she also backed expansions at Luton and Gatwick airports, as well as plans to redevelop Manchester United's Old Trafford football ground.
Ms Reeves described the UK as a country of "huge potential" which had been "held back" for "too long" because politicians lacked the "courage" to challenge the status quo.
"Low growth is not our destiny, but growth will not come without a fight, without a government willing to take the right decisions now to change our country's future for the better," she added.
The Tories welcomed the plans, but leader Kemi Badenoch said it had been stolen from her party. She claimed any prospect of growth would be "destroyed" by the government's Employment Rights Bill.