The investment will cover all the funding grants sought by Birmingham City Council, Advantage West Midlands and Network Rail.
The Department for Transport will provide £160 million to improve the station, in addition to the £128 million already set aside in last year's Rail White Paper.
The Department for Business Enterprise and Regulatory Reform has agreed to fund £100 million, bringing the total Government spending on the scheme to £388 million.
In total the project will cost £550 million with around £200 million coming from commercial investors.
Construction of a new concourse will double the size of the station and all platforms will be served by escalators, which increase from five to 31.
There will also three new entrances to the station from the city centre and new public square.
Network Rail and Birmingham City Council plan to start work in 2009. The project is expected to be complete by 2014.