The Wales international put pen to paper on Friday, extending a deal he had only signed an update to in the summer of 2025, off the back of an outstanding 2025/26 campaign in which he was voted Forest's Player of the Season by supporters and picked up four Player of the Month awards along the way.
Williams featured 53 times in all competitions last term as Forest reached the Europa League semi-finals, and has started both of the club's Premier League fixtures so far this season.
"I'm absolutely delighted," Williams said. "The least I can do now is go out there in every game and give everything to repay the faith shown in me and say thank you.
"I'm the second longest-serving player now and I feel like that time has gone so quickly.
"There has been so much change from when I first joined the club, not just with players but the training ground, the stadium — there has been so much change. That's all to do with the ambition that the owner shows. He wants to be one of the best clubs in England and you can see that with the coaches and the players he has brought in."
Williams also reflected on his personal growth since arriving from Liverpool for around £17m in 2022, a switch that has yielded 163 appearances, four goals and ten assists.
"It feels nice to be the second longest-serving and I'm grateful for it. I feel like I've matured as a person, not just on the pitch, since I've been here; I've become a dad while playing here," he said. "A lot has changed and I feel as though I have become a better person."
The defender closed by thanking the Forest support directly.
"Football is nothing without the fans. This is why we play the game," he said. "To get that buzz every Saturday out there in front of 30,000 people, there's no feeling like it. I'm so grateful for them and the support they have shown me since I've joined the club. I feel as though I've gotten better as each season has gone on, and that's all I can do — repay the fans for the belief shown in me."