In a speech to the Confederation of British Industry conference, which was delayed after he cancelled his appearance on Monday, the PM said: "Believe me, we will end these autumn measures on December 2, when they expire."
Mr Johnson apologised for causing frustration among businesses, saying imposing restrictions goes "completely against every free market instinct I possess".
He told the conference it would be businesses that help "drive our recovery" after the pandemic and pledged to "do whatever it takes" to help industry bounce back from the economic setbacks caused by coronavirus.
At Prime Minister's Questions on Wednesday, Labour leader Sir Keir Starmer said he wanted "some basic honesty" from the PM on whether the lockdown would end in four weeks, regardless of the effect it has on infection rates of coronavirus.
The prime minister has repeatedly said the restrictions will "expire" on December 2 and MPs must vote on whether they should be extended, but Sir Keir asked if they would end "come what may, or will it depend on the circumstances at the time?"
Responding, Mr Johnson said: "These autumn measures to combat the surge, will expire automatically on December 2.
"And we will then, I hope very much, be able to get this country going again, to get businesses, to get shops open again in the run up to Christmas.
"But that depends on us all doing our bit now to make sure that we get the R (value) down.
"I've no doubt that we can, and that we'll be able to go forward from December 2 with a very, very different approach - but, of course, it will be up to the House of Commons to decide, thereafter, what to do."
Sir Keir responded: "Is he saying that if by December 2 the R rate, the infection rate, has not come below 1, and therefore on December 2 the infection rate is still rising, still rising on December 2, is he saying that come what may we will come out of lockdown with infection rates going up on December 2?
"That doesn't seem sensible to me."
Mr Johnson replied: "It is thanks to the efforts of the British people that the R is now currently only just above 1, as it is.
"And we are doing the right and the prudent thing at the right time to get that infection rate down and these measures, as I have said repeatedly to the House, will expire on December 2.
"If he is now saying he wants to expand, protract them beyond December 2, then perhaps he should make his position clear."
The PM's spokesman said it was Mr Johnson's "firm view" that lockdown would end when planned.
He was asked about the difference in Mr Johnson's remarks at the CBI conference, compared with his less definitive words at PMQs.
"I think the PM has been clear on that.
"Legally the regulations which MPs are voting on today will lapse on December 2 and a new regime will be brought into place, subject to a vote.
"You heard what the PM said to the CBI. His very firm view is that it will end on December 2.
"We have said it is our intention to return to a regionalised and localised tiered approach."
MPs are debating the new four-week coronavirus lockdown for England amid warnings the NHS will be overwhelmed with thousands more deaths unless action is taken.
Following the debate there will be a vote in the House of Commons.
Watch MPs debate England's forthcoming lockdown:
The Labour leader asked Mr Johnson to use the lockdown to "fix Test and Trace", adding: "We've been going round and round in circles on this. The latest figures show that 113,000 contacts were not even reached and that's just in one week.
"Only 20% of those who should be isolating are doing so and the majority of people still don't get results in 24 hours."
The prime minister praised the Test and Trace system before adding: "I'm perfectly willing to accept the failings of Test and Trace, of course I am, and of course I take full responsibility for the frustrations people have experienced with that system.
"But to go from 3,000 tests a day, 2,000 tests a day to 500,000 is a quite remarkable feat."