The TV star, 48, who was made an OBE by the Queen in 2019, attended the Westminster Abbey service in his role as head of the worldwide youth organisation.
The monarch, who died at Balmoral on Royal Deeside, Aberdeenshire, on September 8 aged 96, was patron of the Scout Association.
For the ceremony, Grylls swapped his Scouts top and toggle for a black morning jacket with a white shirt, black tie and grey pinstripe trousers.
Following the ceremony, alongside a series of pictures, he tweeted: “It’s a day we will never forget… a truly beautiful testament to our Nation’s Sovereign, Her Majesty Queen Elizabeth. Rest in Peace. Your duty done. Long Live King Charles…”.
The monarch, who died at Balmoral in Scotland on September 8 aged 96, was patron of the Scout Association.
A tweet from the Scouts ahead of the funeral on Monday said: “Chief Scout, @BearGryll, will represent Scouts at State Funeral today and pay final respects to our Patron, HM The Queen.
“Our thoughts are with the Royal Family.”
He was appointed as Chief Scout in 2009, aged 34, making him the UK’s youngest ever Chief Scout at the time, the official Scouts website says.
He went on to become the first-ever Chief Ambassador of World Scouting in 2018, which sees him responsible for promoting Scouting values to a global audience.
Following the Queen’s death, he told the PA news agency that the Scouts family were “united in sorrow for the loss of our Patron” and that she leaves a “bright legacy of hope and promise for future generations”.
Grylls said the Queen had told him several times how she loved volunteering and remembered it as a young girl during the war.
He added that she “championed” young people in the UK throughout her life and was “especially proud” when girls were first able to join the Scouts in the 1970s.
The Queen was also “so generous” to the Queen’s Scouts – the highest award Scouts can receive – every year at Windsor Castle, he said.