The Bracknell & Wokingham swimmer came home in 2:09.44 in a race that saw a world record set by Daniel Gyurta.
It was a fantastic achievement just to get to the final on his debut at an Olympic Games.
Willis said: ""That was tough race and I gave it my all. I'm very happy for Michael - he deserves it 100%. It was great for me to experience as well."
Training partner Michael Jamieson swam the race of his life to win a silver medal, smashing the British record yet again clocking a time of 2:07.4.