MPs will get the chance to make their own tribute to the Queen in the Commons from 12 noon on Friday, before a further session from 2pm on Saturday.
Senior political figures are expected to swear an oath of loyalty to the new King, Charles III, on Saturday, according to the Commons authorities.
All MPs will have an opportunity to take the oath when parliament returns after a 10-day period of national mourning, although this is “not a formal requirement”.
The prime minister – who said the Queen was “the rock” on which modern Britain was built – met with senior ministers and palace officials to begin planning the state funeral.
Ms Truss was informed of the Queen’s death by the head of the civil service Simon Case at about 4.30pm on Thursday as she worked in Downing Street.
After making her statement outside the famous black door of No 10, she spoke by phone with King Charles to offer her condolences.
During a 10-day period of mourning beginning on Friday all government announcements will be paused, but officials will continue to work on Ms Truss’s plan to cap annual energy bills at £2,500 before the looming price hike on 1 October.
Schools will remain open, and sporting and cultural organisations will decide for themselves whether scheduled events should go ahead, No 10 said.
There was an early indication of the monarch’s death in press releases issued by No 10 on Thursday afternoon to announce ministerial appointments.
Downing Street was informed at about 4.30pm that the Queen had passed away, but the information was not made public by Buckingham Palace until 6.30pm.
No 10 tweaked the form of words it uses to make appointments known. Under normal protocol, such announcements are introduced with the words “The Queen has been pleased to approve the following appointments”.
But in a statement released by No 10 at 5.30pm on Thursday, the words used were “On Wednesday 7 September, The Queen approved the following appointments to take effect today (Thursday 8 September)”.
Ms Truss said: “Queen Elizabeth II was the rock on which modern Britain was built. Our country has grown and flourished under her reign. Britain is the great country it is today because of her.”
Labour leader Sir Keir Starmer said the nation mourned the passing of our “greatest ever monarch”. He added: “For 70 years, Queen Elizabeth II stood as the head of our country. But, in spirit, she stood amongst us.”
Commons speaker Sir Lindsay Hoyle said the Queen’s death was a “terrible loss for us all”, adding: “We will miss her beyond measure.”
Outgoing Tory prime minister Boris Johnson said it was the country’s “saddest day” and that the Queen had possessed a “unique and simple power to make us happy”.
Her reign spanned 15 prime ministers and dozens more Commonwealth leaders. She received weekly briefings from the PM of the day and dozens of government documents passed across her desk every week for formal approval.
King Charles admitted he was an “inveterate interferer and meddler” in a BBC documentary in 2018. But he insisted his meddling would not continue when he acceded to the throne.
He said: “No, it won’t. I’m not that stupid. I do realise that it is a separate exercise being sovereign. So, of course I understand entirely how that should operate.”