Ahead of the press conference, Mr Johnson urged UK businesses to “keep going in the way that you have”.
No 10 said he will update the UK on the government’s “steps to defeat” the disease from 17:00 BST.
Meanwhile, Downing Street faces the deadline for its target of 100,000 daily virus tests.
In a tweet, Mr Johnson acknowledged “how hard and stressful it has been to give up even temporarily those ancient and basic freedoms, not seeing friends, not seeing loved ones, working from home, managing the kids, worrying about your job and your firm”.
Speaking directly to businesses, the prime minister said he understood their “impatience”, but added: “I must ask you to keep going in the way that you have kept going so far, so we can protect our NHS and save lives.”
The UK government’s chief scientific adviser Sir Patrick Vallance and chief medical adviser Prof Chris Whitty will appear alongside the PM at Thursday’s briefing.
Mr Johnson, who has just recovered from Covid-19, returned to work in Downing Street this week but missed Prime Minister’s Questions on Wednesday following the birth of his son with his fiancee Carrie Symonds.
Downing Street has insisted the government is “working hard” to hit its target of 100,000 tests per day, but earlier Justice Secretary Robert Buckland admitted it might not be met.
Health Secretary Matt Hancock pledged to reach the goal by the end of April. The latest figures show it reached just over 52,000 coronavirus tests on Tuesday, while testing capacity was at just over 77,000.
A scientist advising the government on testing, Prof John Newton, said he is “pretty confident” the government will hit the target, but warned there will be a lag in the data.
He said it would not be clear whether the target had been reached until the end of the week.
Meanwhile, Downing Street has said social distancing measures will not be relaxed if this would allow the virus to spread “in an exponential way”.
“We are not going to gamble those sacrifices away by taking steps that will lead to an exponential growth in the disease again,” the prime minister’s official spokesman said.
It comes as the Scientific Advisory Group for Emergencies (Sage), which is working on a range of options for easing lockdown restrictions, prepares to meet later. The lockdown is due to be reviewed on 7 May.
Justice Secretary Robert Buckland said Sage would be reporting to the prime minister and to cabinet, with decisions about any easing of the lockdown being made on the basis of the evidence they provided.
However, he added: “Being absolutely frank, I don’t think you’re going to hear specific detail – I think that would be premature.”
Asked about reports the lockdown may be extended until June, the prime minister’s official spokesman said: “What you’ve obviously heard from [the UK’s chief medical adviser] Chris Whitty is that this is a disease that is going to be around for a significant amount of time – he’s said we have to be realistic, we’re going to have to do a lot of things for a long period of time.”
“Let’s not pre-empt the review but, as the PM himself has said, the worst thing we could do is relax the social distancing measures too soon and throw away all of the progress which has been made thanks to the hard work and sacrifice of the British public,” the spokesman added.
Scotland’s First Minister Nicola Sturgeon has said next week may be “too early” to lift the lockdown restrictions “in any meaningful way”.