William, who is president of the Football Association, will be at the final in Berlin as England bid to win their first major trophy since the 1966 World Cup.
The Prince, a noted Aston Villa fan, attended England's Euro 2024 quarter-final victory over Switzerland and their group-stage draw against Denmark.
In a social media post on Saturday, he said: "We are so proud of you all England, just one last push to finish the job!
"Go out there and show the world what you're made of. We believe. W."
William's father, King Charles III, took to social media earlier this week to joke that England should avoid more last-minute drama when they play the final.
In a message to Gareth Southgate's side after Ollie Watkins' late goal secured a 2-1 win against the Netherlands in the semi-finals, Charles sent the players the royal family's "very best wishes" and "warmest congratulations".
He added: "If I may encourage you to secure victory before the need for any last minute wonder-goals or another penalties drama, I am sure the stresses on the nation's collective heart rate and blood pressure would be greatly alleviated! Good luck, England."
England were beaten on penalties by Italy in the last European Championship final in 2021 and have never won the tournament.
In Southgate's eight-year reign, the Three Lions have also suffered narrow defeats in the 2018 World Cup semi-final against Croatia and the 2022 World Cup quarter-final against France.
