Havertz became the youngest player to start a Bundesliga game for Leverkusen when he was named in the line-up to take on Darmstadt on Matchday 10 last season.
The 18-year-old played 24 top-flight games in all during the 2016/17 campaign, and impressed so much, Leverkusen have ensured his immediate future lies at the BayArena.
"I have worked for this moment in the past year," Havertz, who was previously on a youth team contract, told his club's official website.
"It fills me with great satisfaction and pride. I'm happy to finally be set after the last season in which I also had to finish school. Now I have my school leaving exam in my pocket and a professional contract with Leverkusen, it's a great feeling."
Havertz was awarded the prestigious silver Fritz Walter Medal as the country's second-best U17 player in 2016, and Leverkusen's sporting director, Rudi Völler, fully expects him to exploit his enormous potential still further next term.
"Kai has exceptional abilities and is already blessed with a footballing maturity that sets him apart from other players of his age," Völler said.
"He is technically good, dangerous in front of goal, and good with his head. After his great start in professional football, we want to push Kai's development even further. He has huge potential, which will come to the fore even more in the coming years."
Watch: Kai Havertz's Matchday 34 Goal of the Week