Victoria Station, now busier than Heathrow Airport, is to be expanded to cope with rising numbers of travellers at an estimated cost of £500m.
Victoria is one of the capital's busiest commuter stations
A new underground ticket hall will be built and the Tube concourse will be extended by half its size again.
Morning passengers are often locked out of the London Underground (LU) station when platforms become overcrowded.
Tube bosses said work was critical because future modernisation of the station would bring in more trains.
More than 75 million people a year use Victoria Station, each morning about 35,000 people pass through it at rush hour.
Brian Hyland, from engineering consultants Scott Wilson Railways, told BBC News: "The new scheme, when completed, will provide a much safer environment in terms of evacuation, passenger comfort and moving through the station."
The work will start in 2008 and is expected to be completed by 2013.
However, it will not be funded by the controversial multi-billion pound public private partnership (PPP) scheme, which deals only with the renewal and maintenance of the existing Tube system.
Major "congestion-relief projects", like the scheme at Victoria, will be funded by TfL.
Mayor Ken Livingstone has backed it as a "great example" of the investment being put in to improve the Tube.
And Tim O'Toole, managing director of London Underground, said: "Victoria is our most serious problem.
"With this project we are really hoping to get to a point where we are not locking people outside on the street in the rain."