Ferrovial Agroman Laing O'Rourke has secured a contract to build the Northern Line extension by London Underground (LU).
Worth approximately £500 million, the deal, which covers the main construction works, will run for six years.
The extension, from Kennington to Battersea via Nine Elms, could cost up to £1 billion. It is being funded through developer contributions from Battersea Power Station and other developers.
Regeneration work is to be kickstarted in the area, supporting up to 25,000 new jobs and 16,000 new homes, and cutting journey times to the West End and the City to just under 15 minutes.
The rest of the UK also stands to benefit from the project through the jobs created in the supply chain.
Mike Brown, managing director of London Underground, said: "This is an important step in ensuring the delivery of this vital extension which will significantly improve transport links in the area."