She was joined by 16 world leaders, including US President Donald Trump, in Portsmouth to commemorate the 75th anniversary of history's largest combined land, air and naval operation.
Mr Trump, who was on the last day of his UK state visit, said D-Day "may have been the greatest battle ever".
Veterans of the landings in Normandy to liberate western Europe also attended.
Quoting a broadcast by her father, King George VI, at the time of the operation in World War Two, the Queen said the veterans of D-Day demonstrated "more than courage and endurance", showing "unconquerable resolve".
"The fate of the world depended on their success," she said. "Many of them would never return, and the heroism, courage and sacrifice of those who lost their lives will never be forgotten."
She thanked them "with humility and pleasure, on behalf of the entire country, indeed the whole free world".