Kate, 37, wore the Lover’s Knot diamond and pearl tiara with the Queen Mother's sapphire and diamond fringe earrings.
The tiara is sometimes referred to as the Cambridge Lover’s Knot, but it is actually a replica of it, which was commissioned by Queen Mary in 1914 and made by Garrard.
Princess Diana was given the tiara as a wedding gift from the Queen in 1981 and Kate first wore the headpiece in December 2015 for the Diplomatic Reception.
The Queen inherited her mother’s sapphire and diamond earrings after her death in 2002. Kate has worn them once before for a gala event at the Victoria & Albert Museum in 2015.
The duchess and husband William, 36, travelled to Buckingham Palace by car from their residence at Kensington Palace.
Kate teamed the jewels with a white ruffled gown by her go-to fashion designer Alexander McQueen.
She also debuted her Royal Victorian Order, which she was awarded by the Queen in April in recognition of her services to the crown.
This is the tenth time we’ve seen Kate don a tiara. On the last occasion, she wore the Lover’s Knot tiara and Collingwood diamond and pearl drop earrings for the Queen’s annual Diplomatic Reception in December.
The state banquet was held in the Ballroom at Buckingham Palace and will see President Trump and the First Lady sat with members of the Royal Family and around 170 other guests.
Joining Mr Trump and First Lady Melania at the white tie and tiara event were four of Mr Trump's five children - Ivanka Trump, with her husband Jared Kushner, Donald Trump Jr, Eric Trump and his wife Lara, and Tiffany Trump.
Sixteen members of the royal family were at the dinner - the Queen, the Prince of Wales, the Duchess of Cornwall, the Duke and Duchess of Cambridge, the Duke of York, the Earl and Countess of Wessex, the Princess Royal, Vice Admiral Sir Tim Laurence, the Duke and Duchess of Gloucester, the Duke of Kent, Prince and Princess Michael of Kent and Princess Alexandra.
The Duke of Sussex, who joined the Trumps at a private lunch earlier today, was absent from the banquet.
The US president and First Lady arrived at London Stansted airport this morning and were greeted by Foreign Secretary Jeremy Hunt and US ambassador to the UK Woody Johnson.
They were met by the Prince of Wales and Duchess of Cornwall on the lawn of Buckingham Palace, as they stepped off the Marine One aircraft. They were then taken up the steps of the West Terrace to be welcomed by the Queen.
The national anthems of the US and the UK were played, before the president and Prince Charles inspected a Guard of Honour formed by Nijmegen Company, Grenadier Guards.
The Trumps then attended a private lunch with the Royal Family (which also included Prince Harry) followed by a viewing of US exhibits from the Royal Collection at the palace.
Their next stop was Westminster Abbey where the couple laid a wreath at the grave of the Unknown Warrior.
Afterwards the president and first lady enjoyed tea at Clarence House with Charles and Camilla, before returning to Winfield House - the US ambassador’s home in Regent’s Park.