Welsh Secretary Alun Cairns says free-flowing traffic will begin before Christmas – two weeks earlier than planned.
The new road conditions will take effect on December 17.
It currently costs £5.60 to cross one of the bridges into Wales – but it is free to leave. Not paying the toll will save regular commuters up to £1,400 a year.
When the tolls first came into force in the 1960s it was set at a mere 2s 6d – about 12p per crossing.
The first bridge has been in place since 1966 and the second bridge opened in 1996. The newer crossing was renamed earlier this year to the Prince Of Wales Bridge.
Severn bridges in numbers
:: 25 million journeys made across the two bridges each year
:: Prince Of Wales Bridge cost £332m to construct but the eventual repayments totalled more than £1.3bn
:: Annual maintenance and operational costs average £15m between both bridges
:: Additional six million cars a year will cross Severn once tolls are scrapped, government predicts
Mr Cairns made the announcement at the Conservative Party conference in Birmingham, where he said the immediate benefit to Wales would be worth over £100m a year.
He said: “Scrapping tolls before the festive period is an early Christmas present for hard-working commuters who will be £1,400 a year better off.”
In a statement, Prime Minister Theresa May said: “Toll free, free-flow journeys between both communities will drive further economic benefits to all areas surrounding the crossings and the key economic centres in Cardiff, Bath, Bristol, Newport and across to Swansea and West Wales.”