Black-clad MPs stood in silence ahead of a sombre session to remember the Queen, who died yesterday.
A packed House of Commons is paying tribute to the monarch's "magnificent service", with Prime Minister Liz Truss branding her "the nation's greatest diplomat".
Her predecessor, Boris Johnson, said the Queen was "as radiant and knowledgeable as ever" when he last saw her on Tuesday.
The former PM also described her mischievous joy when an unnamed world leader thought she had really leapt from a plane during her famous 2012 Olympics stunt with James Bond star Daniel Craig.
Parliament will also sit tomorrow, with MPs taking an oath of allegiance to the new King from 2pm.
The Queen's death was confirmed shortly after 6.30pm yesterday, and a 10 day mourning period began at midnight in memory of the 96-year-old.
Speaker Sir Lindsay Hoyle, wearing his mourning dress, paid tribute to her "magnificent service", saying: "Almost all of us in the House have experience no other monarch on this country's throne."
The new Prime Minister, who was one of the last people to meet the Sovereign when she travelled to Balmoral on Tuesday, told MPs: "Her late majesty, Queen Elizabeth II, was one of the greatest leader the world has ever known."
You can leave your tributes to Queen Elizabeth II here
Ms Truss referenced the Queen's pledge at age 25 to serve the nation, adding: "The whole House will agree, never has a promise been so completely fulfilled. Her devotion to duty remains an example to us all."
She recalled seeing the monarch charm some of the world's leading investors at Windsor Castle in October last year, and of her last meeting this week said: "She generously shared with me her deep experience of government even in those last days."
Mr Johnson, who also saw the Queen for the last time on Tuesday when he resigned as Prime Minister, said: "A few months ago the BBC came to talk to me about Her Majesty.
"They requested that I should talk about her in the past tense, and I'm afraid to say I choked up, I couldn't go on.
"I'm not easily moved but I was so overcome with sadness that I had to ask them to go away."Describing their last meeting, Mr Johnson said: "She was so radiant and knowledgeable and fascinated by politics as ever and as wise in her advice as anyone I know."
He also described the monarch's mischievous joy when he told her that a "leader from the Middle East" had believed she had jumped from a plane ahead of the 2012 Olympics in the famous stunt alongside James Bond star Daniel Craig.
Labour leader Sir Keir Starmer also delivered a powerful tribute, saying: "Our Elizabethan age may be over, but her legacy will live on forever."
He said: "The late Queen would have wanted us to redouble our efforts to turn our collar up and face the storm... it's in these moments that we must pull together."
He said that "beautiful tributes" from around the world showed the esteem the monarch was held.
Mr Starmer said: "The reason our loss feels so profound is... because in spirit she stood amongst us," he said.
He concluded: "May the Queen rest in peace. God save the King."
Mr Johnson's predecessor, Theresa May, said that the Queen was the most impressive world leader she had ever met.
She described her weekly meetings with the Queen as "special" and said she fondly recalled weekends at Balmoral, stating: "She'd take an interest in what books were placed in our rooms and she didn't always want to be the centre of attention."
Recalling a picnic at Balmoral, Mrs May recalled a faux pas while "mucking in" and transferring cheese from hampers onto the tables.
"The cheese fell on the floor. I had a split second decision to make," the ex-PM recalled to loud laughs.
"I picked up the cheese, put it on the plate and put it on the table. I turned around and saw my every move had been watched very carefully by Her Majesty the Queen.
"I looked at her, she looked at me and she just smiled, and the cheese just remained on the plate."
Ex Labour Party leader Ed Milliband paid tribute to the Queen's humour, saying he had attended a ceremony at Buckingham Palace when his wife Dame Justine Thornton had the honour bestowed on her.
"She (the Queen) just fixed me with a gaze and said: 'Oh, it's you.'
"She said: 'What are you doing here?' She knew full well why I was there, we had a wonderful conversation."
Dame Margaret Beckett, Labour, said that as a newly-elected MP in 1975, she was tasked with writing daily to the Queen in her role as a junior government whip.
"It seemed there was very little point in telling her the things that she already knew from her red box or from the Daily Telegraph. What I wrote about was the things I thought she wouldn't get from these sources, I wrote about the gossip, I wrote about some of the rows."
This came to an end, however, when the monarch went on an overseas visit, and her letters were read by an official in Downing Street.
"I heard many years later that perhaps Her Majesty regretted the return to the original source (of letters)."
Former Tory Northern Ireland Secretary Theresa Villiers described a 2014 visit to Belfast which also saw the Queen visit the set of Game of Thrones.
"Politely and probably wisely she declined the opportunity to sit on the Iron Throne," the MP told the House.
Meanwhile Labour's shadow Foreign Secretary David Lammy drew laughs as he recounted nearly falling asleep in the Queen's presence.
He said joining the Privy Council in November 2008 stuck in his mind.
Mr Lammy recounted: "On that day I was very very sleepy indeed. I was sleepy because my friend Barack Obama had become President of the United States the day before.
"I'd not slept when I got to Buckingham Palace at 6pm. I knelt on the footstall, my eyes closed, I headed towards the Queen's lap.
"She reached out and put her hand on my bald head."
Labour deputy leader Angela Rayner said: "To us she was our Queen, our national figurehead."
She added: "She was an example of leadership to women everywhere."
Tory Mark Francois told the Commons: "She was the most famous person in the world, and probably the most popular."
SNP Westminster leader Ian Blackford said: "I was fortunate to meet the Queen on a number of occasions and was always been struck by the strength, the intellect, the modesty, the humility and often the humour with which she approached her Royal duties."
Referring to Balmoral, where the Queen was staying when she died, Mr Blackford said: "It is well known that Balmoral, with its beautiful and atmospheric scenery, was the Queen’s favourite home.
"Balmoral was a place where she was able to enjoy freedom, peace and an ability to indulge her love of the great outdoors; whether that was walking with her dogs, riding on horses, hosting picnics and BBQs – or from behind the wheel of her Landrover."
Sir Roger Gale, Conservative MP for North Thanet, said: "Those of us who had the privilege of meeting Her Majesty face-to-face without exception, I think, all remember what has been referred to over and over as the twinkle in those beautiful eyes and the smile that is now lighting up heaven."
Cabinet members dressed in black as they met this morning, while Labour's shadow cabinet also met to discuss the monarch's passing.
A Labour Party spokesman said earlier today: ""The shadow cabinet met at 9.30 this morning in Richmond House on the parliamentary estate.
" Keir Starmer led tributes to HM Queen Elizabeth II and the whole shadow cabinet stood in silent tribute to the late Queen."
In a speech last night, Ms Truss said: "Queen Elizabeth II was the rock on which our country was built.
"Britain is the great country it is today because of her."
The PM described the Queen as the "very spirit of Great Britain" and promised: "That spirit will endure."
Speaking on only her third day in office, Ms Truss recalled meeting the Queen on Tuesday when she invited her to form a Government in her name.
The PM said: "She has been a personal inspiration to me and to many Britons. Her devotion to duty is an example to us all.
"Earlier this week, at 96, she remained determined to carry out her duties as she appointed me as her 15th Prime Minister."
Earlier today the Government published new guidance for national mourning as the country marks the passing of the Queen.
A 10-day mourning period began at midnight on Friday, with public-facing Government activity all but suspended and Parliament expected to rise once tributes have been paid.
The state of mourning is due to culminate with the State Funeral, although a date has not been confirmed by Buckingham Palace.
A new five-page Cabinet Office document sets out advice for businesses, events organisers and Brits wishing to pay their condolences after the death of our longest serving monarch.
It states: "Mourning is very personal and we anticipate individuals, families, communities and organisations may want to mark Her Majesty’s demise in their own way.
"There is no expectation on the public or organisations to observe specific behaviours during the mourning period."
