Darlow has made 25 appearances during his Forest career and has been the Championship club's first choice since January.
The 22-year-old has now been rewarded with a new contract and Darlow is happy to be making his mark at the City Ground.
"I am delighted. I have been here a while and it is nice to extend that," Darlow told the club's official website.
"I love the club, I want to keep doing what I have been doing. As a club I want us to progress and I'd like to hold on to the No.1 shirt for another four years.
"The club were happy with how I performed last season. I am a young keeper, but the manager says he is pleased with me, so I just want to keep doing what I have been doing."
Forest boss Billy Davies added: "It's thoroughly deserved, we're all delighted for him."