The West Sussex airport will bring its emergency runway into routine use under the expansion scheme.
Gatwick Airport’s £2.2 billion second runway plan has been given the go-ahead by Transport Secretary Heidi Alexander.
In the privately-financed project, the West Sussex airport will move its emergency runway 12 metres north, enabling it to be used for departures of narrow-bodied planes such as Airbus A320s and Boeing 737s.
This will enable it to be used for about 100,000 more flights a year.
Ms Alexander backed the scheme as a “no-brainer” for economic growth, a Government source said, suggesting flights could take off from the new full runway before 2029.
The Cabinet minister is satisfied with adjustments made, covering issues such as noise mitigation and the proportion of passengers who would travel to and from the airport by public transport.
The Planning Inspectorate initially rejected the airport’s application and earlier this year recommended Ms Alexander should approve the project if the changes were made.
Gatwick says its plans will create £1 billion per year in economic benefits, and generate an additional 14,000 jobs.
A Government source told the PA news agency: “The Transport Secretary has cleared Gatwick expansion for take-off.
“With capacity constraints holding back business, trade and tourism, this is a no-brainer for growth.
“This Government has taken unprecedented steps to get this done, navigating a needlessly complex planning system, which our reforms will simplify in future.
“It is possible that planes could be taking off from a new full runway at Gatwick before the next general election.
“Any airport expansion must be delivered in line with our legally binding climate change commitments and meet strict environmental requirements.”