Holidaymakers will be able to use the NHS app to prove they have had their jab when foreign travel reopens on May 17.
Portugal, Gibraltar and Israel were among 12 destinations announced as part of the Government's green list, allowing people to take sunshine breaks without quarantining.
Transport Secretary Grant Shapps said people who have had both doses of the jab would be able to use their NHS smartphone app as a vaccine passport.
Downing Street suggested earlier this week that the app might not be ready in time, raising questions about how sun-seekers could prove their vaccine status.
But Mr Shapps told a Downing Street press conference that the digital certificates would be available.
People who don't have a smartphone will be able to get a paper certificate.
However holidaymakers face big queues at the borders as staff scramble to deal with extra paperwork - with checks to take up to 15 times longer than normal.
Border Force chief Paul Lincoln warned that checks that normally take 30 seconds could now last for up to 10 minutes.
He said: "Unfortunately we are not back to normality yet. Travel will be different and, as the Transport Secretary says, we still need to be cautious.
"There will continue to be additional health checks for every person crossing our border and inevitably that means it will take longer for most people to enter the UK.
"These measures have been put in place to protect the hard-fought gains and sacrifices that have been made by individuals and society in the UK, minimising the risk of importing variants while protecting the success of our vaccine rollout."
Australia, New Zealand, Singapore, Brunei, Iceland and the Faroe Islands and the Falklands are also on the green list.
These countries join the remote territories of the Falklands, South Georgia and the South Sandwich Islands, Saint Helena, Ascension Island and Tristan da Cunha.
But people will not be able to go on holiday to Australia, New Zealand or Singapore as they are closed to UK tourists.
Mr Shapps said the lifting of restrictions was "necessarily cautious" to avoid derailing the UK's progress against Covid-19 by importing the virus from abroad.
He said: "We in this country have managed to construct a fortress against Covid. But the disease is still prevalent in other parts of the world, most notably at the moment in India.
"In fact, more new cases of Covid have been diagnosed around the world in the last seven days than at any time since the pandemic began."
He added: "That's why today's announcement, removing the stay in the UK restrictions from May 17, is necessarily cautious.
"We must make absolutely sure that the countries we reconnect with are safe, that their infection rates are low and their vaccination rates are high.
"It means making sure we are not incubating the most dangerous variants that they're not and that they have safe and secure surveillance in place."