The Hoops have to overturn a 2-0 first-leg deficit at Celtic Park or fail to reach the group stages which would be worth around £7.5m to the club.
He said: "This is one of the biggest games of my life - so much is at stake.
"So much depends on this game and there is so much pressure on myself and my team-mates. Hopefully we can thrive on it and go from there.
"We want to play in the Champions League, it's a fantastic competition. Last season was one of the best in our careers and hopefully we can qualify again."
The defeat in Kazakhstan came as a shock, Andrei Finonchenko and Sergey Khizhnichenko scoring the goals for Karagandy.
Ledley said: "We were surprised by them? Not really. We did our homework and knew they were going to be well organised and dangerous on set-plays. That's where the first goal came from, a long throw.
"They are a big team and dangerous from set-plays. But we can't let that get inside our head. We just have to play the way we would normally.
"They didn't really surprise us as we knew they were going to be a good team and they proved that.
"We dominated possession in the first game and they sat in. I'd be surprised if they came out and attacked in the second leg but whatever formation they play we need to be able to break them down.
"Everyone would want an early goal but we scored two against Inverness at the weekend pretty late, and as long as we get two or three, and do not concede, I will be happy."
Ledley says the home fans will create an intimidating atmosphere. And the pageantry that has come to be known as the hallmark of such occasions at Celtic Park was last week safeguarded when the club reversed plans to break up the controversial Green Brigade group after receiving assurances they would improve their behaviour.
"The fans' role is massive," he said. "They have been brilliant ever since I've been here and I'm sure the fans will be exactly the same against Karagandy.
"The Old Firm is a fantastic atmosphere but when it's the Champions League, I don't think anything can beat it. The day we played Barcelona was one of the greatest moments of my life and the atmosphere was fantastic that night.
"I think the Green Brigade are fantastic. They bring the atmosphere to Celtic Park and without them, it wouldn't be so good.
"My family come up and all they talk about is the Green Brigade. They set the atmosphere alight."