The Labour leader will make a televised statement at 4pm to address his critics after Durham Constabulary launched an investigation into allegations he broke lockdown rules in April 2021.
A beer-and-curry gathering in April 2020 is facing an inquiry after Sir Keir had a meal and alcohol indoors with party staff when Covid rules outlawed households mixing indoors.
He has found himself dodging journalists' questions since last Friday when the police investigation was launched after he previously demanded Prime Minister Boris Johnson resign for being given a fixed term penalty notice.
The Opposition leader said Mr Johnson has lost the trust of the public after being found guilty of breaking Covid regulations and that his position was untenable.
Durham police's investigation into Sir Keir's own actions has placed the Holborn and St Pancras MP in a precarious situation whereby he risks being accused of hypocrisy if he is fined for breaking the rules himself without then quitting his position.
The Labour chief is thought to be planning to use his statement to pledge to stand down if he is handed a fine.
Party insiders say he feels he has no other alternative after his public demands of the Prime Minister.
Sir Keir continues to insist he followed the rules on all occasions.
Labour says the food was consumed between work events, meaning it was within the rules despite the ban on indoor socialising.
In a TV clip on Friday, the only time Sir Keir has spoken about the launch of the police investigation, the party leader said he was "confident there was no breach of the rules".
"I was working, I stopped for something to eat. No party, no breach of the rules," he added.
"The police, obviously, have got their job to do, we should let them get on with it, but I’m confident that no rules were broken."
Amid the growing pressure on him to clarify his position, the former director of public prosecutions last night pulled out of an event taking place at the Institute for Government today.
He also did not attend a memorial service for former MP James Brokenshire at St Margaret's Church in Westminster, where he was expected join politicians from across the divide including the Prime Minister and Cabinet members.