The City of London Corporation has agreed to make a direct contribution of £200 million to the Crossrail project.
In addition, the City Corporation will seek contributions from businesses of £150 million, and has guaranteed £50 million of these contributions.
Mayor of London Boris Johnson said: “This is a crucial milestone and, with funding committed and agreements in place, the pace of delivery will now quicken - with Crossrail transferring to TfL tomorrow, work at Tottenham Court Road beginning in the spring, and delivery partner companies being appointed early next year.”
The Government has pledged £5.6 billion for the new line, which will run from Maidenhead to the west of London to Shenfield and Abbey Wood in the east.
Network Rail will contribute a further £2.3 billion.
Last month Spanish-owned airports operator BAA became the first company to throw money into the pot for the £16 billion scheme.
It is contributing £230 million to the cost in exchange for regular services to London’s Heathrow airport.