The Prime Minister will spell out his strategy in the Commons, with areas in England labelled as medium, high or very high risk, which will inform the "appropriate interventions" needed in each area.
Downing Street said "this is a critical juncture" and it is "absolutely vital" that everyone follows the clear guidance set out to help curb the spread of coronavirus.
The Prime Minister is chairing a meeting of the Government’s COBR committee at 8am to finalise what will be announced in Parliament.
Mr Johnson is then expected to announce the new three-tier strategy in the Commons at 3.30pm.
This will be followed by a Downing Street press briefing at 6pm, led by the Prime Minister, Mr Sunak and Prof Whitty.
Watch: Oliver Dowden explains new three-tier Covid restrictions
What will the Prime Minister say in his speech?
Many details are yet to be confirmed but leaders in Liverpool said pubs and bars, betting shops, casinos, and gyms would close under the third tier restrictions, while reports also suggest people will have to avoid all non-essential travel and to not travel between areas.
Merseyside is expected to be among the areas subjected to Tier 3 restrictions – but there is still disagreement about a financial support package for the area should harsh measures be imposed.
According to Tees Valley mayor Ben Houchen, the restrictions are expected to last for four weeks at a time.
The Prime Minister is expected to say Tier 1 restrictions are the baseline restrictions in place across England, including a 10pm hospitality curfew and a ban on most gatherings of more than six people.
Tier 2 restrictions are expected to be similar to rules currently in place in Middlesbrough and parts of the north east, where indoor mixing of households is not allowed.
Two households may be allowed to meet in a private garden, as long as the rule of six and social distancing are followed.
It is not yet clear how an area will be placed into a tier, or to what extent regulations will be written and enforced locally.
What else is happening today?
A data briefing with deputy chief medical officer Jonathan Van Tam is being held at 11am.
He is expected to set out the latest data on the spread of coronavirus in the UK before the Prime Minister makes his speech at 3.30pm.
Cabinet minister Oliver Dowden has said that tough new coronavirus restrictions may be needed until after Christmas.
Mr Dowden told Sky News: "If those measures are successful we hope to be able to take areas out of those high levels of restrictions.
"The purpose of doing this is to ensure we get the virus under control so by the time that we get through to after Christmas we are in that position where it is under control.
"Indeed I hope it will be sooner than that."
Mr Dowden was also asked how areas could come out of tougher measures. He said it was down to getting infection rates under control.
He said the new tier system would be “empowering local leaders” to decide what further restrictions might be needed and on enforcement.
Watch: What is long COVID?