The Prime Minister’s official residence was covered in St George’s flags which were draped across windows.
England bunting has also been hung from lampposts and gates.
The PM was also pictured holding his own flag outside his front door, as he gave the camera a thumbs up in preparation for the big game.
England will take on Italy in the European Championship final this Sunday.
Mr Johnson has faced pressure to consider a one-off day off if the Three Lions in the tournament.
Asked during a visit to energy company Bulb’s central London headquarters on Thursday about the prospect of a bank holiday if England beat Italy in the final, Mr Johnson said: “I think that would be tempting fate; let’s see what happens.”
More than 346,000 people have signed a petition calling for Monday off work, arguing that it would be "beneficial and sensible to give the country the day off the next day if England win".
It reads: “Sunday 8pm is a difficult time for families to plan to be together for the event – knowing we have an additional day off the next day would significantly help this.
“Furthermore, a historic win should be celebrated. It would be expected for the winning team to parade the trophy, and a bank holiday would be a perfect time to do this.
“Also, English people would naturally want to continue to enjoy the win, giving the retail and leisure industry a much-needed opportunity to make up lost revenues.”
Schools and businesses are already planning on opening late on Monday to allow fans to recover from a late night.
Many bosses have decided to allow staff a lie-in on Monday morning if the Three Lions beat Italy.
Downing Street has said it will set out any celebrations such as a victory parade for the England team “in due course”.