According to the team, the deal has an average annual value of $925,000.
Zacha, 18, was the only 2015 first-round selection that was not either not signed or planning to play in the NCAA.
Zacha weighed in on the deal after coming to terms (Aug. 11).
"All the time I trusted my agent. He told me everything would be okay," Zacha said. "I had some good talks in New Jersey with the GM. It was just a matter of time until the contract was coming."
As far as whether Zacha will play in the NHL this season, Devils GM Ray Shero weighed in.
"I don't know," Shero said. "One day he will. Whether it's going to be this year or in the future, we're not sure. I'm not leaning one way or the other. It's a decision he makes for us at some point."
In 37 games with the OHL's Sarnia Sting last year, Zacha recorded 16 goals and 18 assists. He also had two points in five games for his native Czech Republic during the 2014 IIHF World Junior Championship.