"I can serve notice now that by the end of September when all over 18s will have had their chance to be double jabbed, we're planning to make full vaccination the condition of entry to nightclubs and other venues where large crowds gather," Mr Johnson said.
"Proof of a negative test will no longer be enough."
The announcement came after nightclubs across the country opened their doors from midnight on Sunday.
Some 35 per cent of 18 to 30-year-olds - three million people - remain unvaccinated, and the Prime Minister told the press conference: "Some of life's most important pleasures and opportunities are likely to be increasingly dependent on vaccination."
Professor Jonathan Van-Tam also acknowledged the sacrifices made by young people during the pandemic, including the lengthy lockdown of nightclubs.
But England’s deputy chief medical officer warned: “On the science side, however, it is a case in point that if you pack my garden shed full of people and they are unvaccinated, the likelihood of transmission is going to be far greater than if you pack my garden shed full of people who have been fully vaccinated and are 14 days out the other side of their second dose.
“It will not reduce the risks to zero – nothing reduces the risks to zero other than standing in a meadow completely on your own ad infinitum with nobody coming within three metres of you.”
Sir Patrick Vallance was forced to correct an answer to a member of the public’s question when he incorrectly stated that 60 per cent of hospitalisations were fully vaccinated. He later tweeted the correct statistic that 60 per cent of hospitalisations were from people who were completely unvaccinated.
A leading industry body reacted with horror to the proof of vaccination plans for nightclubs, branding them an “absolute shambles”.
Michael Kill, chief executive officer of the Night Time Industries Association (NTIA), accused the Government of "another chaotic U-turn".
"So, 'freedom day' for nightclubs lasted around 17 hours then," he said, noting the announcement came on the day nightclubs across England reopened.
"The announcement from the Prime Minister that Covid passports will be made mandatory for nightclubs in September comes after his Health Secretary said only one week ago that they would not be compulsory. What an absolute shambles.
"Leaving aside the fact that this is yet another chaotic U-turn that will leave nightclubs who have been planning for reopening for months will now have to make more changes to the way they operate - this is still a bad idea.
"Eighty per cent of nightclubs have said they do not want to implement Covid passports, worrying about difficulties with enforcing the system and a reduction in spontaneous consumers, as well as being put at a competitive disadvantage with pubs and bars that aren't subject to the same restrictions and yet provide similar environments."
Labour’s deputy leader Angela Rayner said the Government’s Covid passport policy was a “total mess”.
She tweeted: “The make it up as you go along Covid passport policy is a total mess. How can I be safe to go clubbing tonight but I need a Covid passport in September? Why are hospitality staff being expected to uphold the law because the government has washed their hands of responsibility?”
Mr Johnson defended the timing of lifting England's coronavirus restrictions despite the rising cases.
He argued that not opening up now, with the "firebreak" offered by the school holidays, meant the risk of even tougher conditions in the colder winter months.
He said: "There comes a point after so many have been vaccinated when further restrictions no longer prevent hospitalisations and deaths but simply delay the inevitable.
"So we have to ask ourselves the question: if not now, when?"
The Prime Minister also said people had to accept that increasing numbers would be required to self-isolate "as a consequence of living with Covid".
"I know how frustrating it is for all those who have been affected or pinged,” he said.
But people identified as contacts were "at least five times more likely to be infected than others".
"Even if they have been vaccinated there is a significant risk that they can still pass the disease on.
"And so as we go forward I'm afraid that the continuing sacrifice of this large minority, those of us who have been asked to isolate, remains important to allow the rest of society to get back to something like normality.
"I'm afraid that at this stage it's simply a consequence of living with Covid and opening up when cases are high in the way that we are."
The Government's chief scientific adviser Sir Patrick Vallance said there were "high levels of Covid and they are increasing".
He said the UK was quite close to the previous "winter wave" of infections.
He told the Downing Street briefing: "In the winter wave, we were up to around 60,000 people testing positive per day. We are now somewhere on towards 50,000. So we're quite close to the size of the winter wave of infections and this is going to increase."
Discussing hospital admissions, Sir Patrick said it was "a somewhat different picture" as the numbers are expected to increase, although not to the same extent as before.
"We do expect there to be over 1,000 people per day. Being hospitalised with Covid because of the increase in infections, but the rates should be lower than they have been previously because of the protective effects of vaccination," he said.