Gatwick Airport passengers are to be served by 11 extra boarding gates.
Planes can pass under the bridge with two-and-a-half metres to spare
Transport secretary Alistair Darling opened the Pier 6 development on Monday, describing it as "a terrific new facility".
It is connected to Gatwick's North Terminal by a 32m high footbridge and will be in use by the end of the week.
Work on the £100m building began in 2003 and it offers 11 new pier-served aircraft stands so travellers need not go outside to reach their plane.
It is estimated that 92% of North Terminal passengers will have access to this pier stand boarding, saving around 55,000 transfer-bus journeys a year.
British Airways is the first airline that will use the stands.
Mr Darling said: "This bridge will make it easier for passengers to pass through the airport while reducing the airport's impact on the environment."
Mike Clasper, chief executive of airport operator BAA, said: "This major new landmark for Gatwick sets the stage for a positive future for the airport at a time when passenger numbers are booming."
The new building will also provide shops, cafes and other amenities.
Pier 6 and its pedestrian link have constituted the biggest development at Gatwick since the opening of the North Terminal itself in 1988.
The bridge, which is 197m long, was lifted into place in May 2004 over the course of 10 days.
Three million passengers are expected to use its travelators and walkways every year.
It is also high enough to accommodate taxiing Boeing 747 jumbo jets passing underneath.
The footbridge was the first of its kind built in the UK and larger than the only other one in the world, at Denver International Airport in the US.