The Germany Under-21 international joined Leverkusen in 2011 after spending three seasons with Stuttgart's reserve team.
Leno has since gone on to establish himself as a first-team regular at the BayArena, helping Sami Hyypia's side to secure a place in the Champions League as Leverkusen finished third in the Bundesliga last season.
And the 21-year-old is confident the club will continue to enjoy success in years to come.
"Bayer 04 Leverkusen took me on as a 19-year-old third division keeper and turned me into the number one at a club in the Champions League," Leno told the club's official website.
"I was really impressed with the massive vote of confidence back then and I'm incredibly grateful to the club for that.
"We've been successful together over the past two years and I've been able to improve consistently due to the constant domestic and international challenges and thanks to the top class training with an outstanding team.
"I'm sure I will continue my development here in the future as the club provides the optimum conditions. And the fact that a player like Lars Bender has just signed a long-term deal at Bayer 04 is a clear signal to the rest of the lads.
"This team can go a long way."