Cahill has made a timely recovery from the hamstring injury he suffered early in the second leg of Chelsea's Champions League semi-final in Barcelona and, with captain Terry and fellow defender Branislav Ivanovic both suspended, he expects to line up alongside David Luiz in central defence.
After missing the FA Cup final triumph against Liverpool earlier this month, England international Cahill admits he was determined to feature at the Allianz Arena this week and his return is a major boost to Blues interim manager Roberto Di Matteo.
"That was a massive blow to me to miss the FA Cup. I was sick when I got the injury because I knew that would be the case straight away," Cahill said.
"That would have been a big moment in my career so to make this one will be huge.
"I always had the goal to be fit for this game and thankfully it has healed quickly."
Di Matteo is relieved that Cahill and Luiz will be able to start against Bayern, but the Italian could still be forgiven for feeling nervous about how the pair, who have played together only occasionally since Cahill's January move from Bolton, will cope with Bayern forwards Franck Ribery, Arjen Robben and Mario Gomez.
However, Di Matteo will have been impressed to hear Cahill insist that he is up to the task of standing in for the demonstrative Terry and expects no problems forming a solid defensive wall with Luiz.
"With the quality John has and the leadership he carries around, he is a big presence in our squad. But I speak when I am on the pitch as well, that is how I am," Cahill said.
"There will be some experienced players out there. We will just go and do the job we are supposed to do regardless of if he is playing or not.
"He won't be playing but he will be there in our dressing room and will be a big part of the day.
"I have played with him (Luiz) before and he is a fantastic player. It's easier playing with good players. He is a Brazilian international. I don't see it being a problem."
Playing for Europe's elite club prize in his first major final could easily give Cahill sleepless nights as the match draws nearer, but the 26-year-old seems remarkably relaxed about appearing on such a grand stage.
"It's a huge game, everyone knows how big it is. But for us, if we get caught up in that, and start thinking about stuff apart from the game it will be a distraction," he said.
"We have to address it in the same manner as those big games we did well in earlier in the season."
Cahill's Chelsea career started slowly as he struggled to impress former boss Andre Villas-Boas and spent several weeks on the bench.
But, just five months later, he has a chance to end a "mad" season by helping Chelsea win their first Champions League title in his first major final.
"I couldn't tell you when I last played in a final, probably at junior level," he said.
"I won a few trophies as a kid but it would be my first medal at senior level.
"It's been a mad season, a fantastic season. Going into this huge game in my first six months is really crazy.
"Ideally you want to come in and hit the ground running and have everyone saying you are amazing, but that doesn't always work.
"Moving in that January transfer window is different to moving during the summer. You are juggling everything behind the scenes as well as trying to concentrate on your football.
"It was a tough first few weeks but I was always hoping my form would come good.
"You come to big clubs to play in these competitions and now we have a great chance to lift one of the big trophies in club football."