The long-awaited line fell years behind and went over budget – but is finally set to open.
Services will initially operate from Mondays to Saturdays, allowing further testing and software updates to take place on Sundays.
Crossrail – the project to build the new east-west railway – was due to be completed in December 2018 and was set a budget of £14.8billion in 2010.
But it has been hit by numerous problems including construction delays and difficulties installing complex signalling systems.
The total cost of the project has been estimated at £18.9billion, including £5.1billion from the Government.
It is hoped the Queen – who the line is named after – will be involved in the opening.
TfL commissioner Andy Byford said: “I am delighted that we can now announce a date for the opening of the Elizabeth line in May.
“We are using these final few weeks to continue to build up reliability on the railway and get the Elizabeth line ready to welcome customers.
“The opening day is set to be a truly historic moment for the capital and the UK, and we look forward to showcasing a simply stunning addition to our network.”
Mayor of London Sadiq Khan said the Elizabeth line will make London “safer, fairer, greener and more prosperous”.
He went on: “This is the most significant addition to our transport network in decades, and will revolutionise travel across the capital and the South East – as well as delivering a £42 billion boost to the whole UK economy and hundreds of thousands of new homes and jobs.
“Green public transport is the future, and the opening of the Elizabeth line is a landmark moment for our capital and our whole country, particularly in this special Platinum Jubilee year.”
Signage on display at the Paddington Elizabeth Line Station Jonathan Brady
A Transport for London employee stands on the platform at the Canary Wharf Elizabeth Line Station Jonathan Brady