The portrait, by Ranald Mackechnie, was taken in the Victoria Vestibule at Windsor Castle earlier this year.
In her Jubilee message the monarch thanked people for organising events to celebrate her milestone, saying “many happy memories” would be created.
Millions are gearing up for street parties to mark 70 years on the throne over the four-day bank holiday weekend.
There are also a series of official events starting with Thursday’s Trooping the Colour parade and ending on Sunday with a Jubilee Pageant through London.
The specially commissioned portrait pictures show the Queen looking contented, sitting on a cushioned window seat at the castle which has been her main home for the last couple of years. The historic residence’s famous Round Tower is visible in the distance.
Mr Mackechnie took two previous portraits of the Queen alongside the Prince of Wales, the Duke of Cambridge and Prince George to mark her 90th birthday in 2016.
In her Jubilee message the monarch said: “I continue to be inspired by the goodwill shown to me, and hope that the coming days will provide an opportunity to reflect on all that has been achieved during the last 70 years, as we look to the future with confidence and enthusiasm.”
The traditional Trooping the Colour parade to mark the Queen’s official birthday will involve more than 1,500 officers and soldiers and 350 horses from the Household Division, as well as an RAF flypast.
The 96-year-old monarch, who has mobility issues and has recently cancelled several public appearances, is likely to join members of the Royal Family on the balcony at Buckingham Palace to watch the display.
The Duke and Duchess of Sussex will watch the parade, although they will not appear on the balcony.
The couple, who now live in the US, will have a prime vantage point from the Duke of Wellington’s former office, overlooking Horse Guards Parade, where they will watch Prince Charles inspect the guardsmen and officers and take their salute in his mother’s place.
They are travelling with their children Archie, three, and Lilibet, who turns one on Saturday. Lilibet is the Queen’s family nickname.
The Queen’s son Prince Andrew, whose royal titles were returned to the Crown amid a lawsuit in the US, will not be present.
For any big family gathering there are questions to smooth out before it gets started. Like who is going to be there.
There’s been speculation about when we might see the Queen over the Jubilee weekend.
A couple of events will be her priorities – and Thursday’s Trooping the Colour and the Buckingham Palace balcony will be one of them.
Although it will be Prince Charles who inspects the troops, taking on another ceremonial task.
It’s been made clear that Prince Andrew won’t be at this first showcase event.
But Prince Harry and Meghan, although very publicly not invited on the palace balcony, will be watching with other members of the Royal Family through windows above Horse Guards Parade.
It looks a bit like a balcony, so maybe it’s building bridges one step at a time.
After all that planning, the celebrations and the long holiday weekend can finally begin.
On Thursday evening, more than 3,000 beacons will be lit across the UK and the Commonwealth in tribute to the Queen, with the Tree of Trees beacon illuminated outside the palace.
The monarch is to lead the lighting of the principal Jubilee beacon in a special ceremony at Windsor Castle, Buckingham Palace said.
Also on Thursday the Prince of Wales and Duchess of Cornwall will guest star in an episode of TV soap EastEnders, on BBC One at 19:30 BST.
Prince Charles and Camilla join the residents of Albert Square at their jubilee street party.
At a service of thanksgiving at St Paul’s Cathedral on Friday, there will be other accommodations made for the Queen’s comfort, with no ceremonial journey to the event.
If the monarch does attend, she will use a different entrance rather than scaling the steps.
And it is not certain she will make the planned trip to Epsom for the Derby on Saturday.
On that evening, the BBC’s Party at the Palace concert – set on three stages in front of Buckingham Palace – will see Diana Ross, George Ezra, Alicia Keys and Nile Rodgers entertain a live crowd of 22,000 people and a television audience of millions.
At the concert, heir to the throne Prince Charles and his son, the Duke of Cambridge, will pay tribute to the Queen who will be watching on television.
On Sunday there will be street parties, picnics and barbecues across the UK with more than 85,000 Big Jubilee Lunches planned.
The finale of the weekend will be the Jubilee Pageant which will make its way through the streets of the capital with a cast of 6,000 performers and close to 200 celebrities.
It will end with Ed Sheeran singing the national anthem with a choir made up of “national treasures” outside Buckingham Palace.
Ahead of the celebrations, the Queen took a short break at Balmoral Castle, in Aberdeenshire, but returned to Windsor on Tuesday.
Saturday is the first birthday of Harry and Meghan’s daughter Lilibet – who is named after the Queen’s family nickname.
The Queen’s granddaughter Princess Eugenie has led tributes to her in an article in the Spectator, describing her “grannie” as “a woman who has transcended time and has been that constant rock for so many when the world can feel so fragile”.
She said she would love her son August to “have her patience, her calmness and her kindness, while always being able to laugh at himself and keep a twinkle in his eye”.
Scotland’s First Minister Nicola Sturgeon congratulated the monarch on a “lifetime of service” and urged all Scots to mark her “values of integrity, wisdom, justice and compassion” – regardless of their views on the British monarchy.
Not everyone will be celebrating the occasion. Anti-monarchy campaign group Republic said a recent poll had shown the British public “just aren’t that bothered about royal events”.
Speaking for the group, Graham Smith said: “The Jubilee is not a national celebration, it is a carefully staged event to promote the monarchy and the royal brand.”