The Brazilian's new deal will see his stay at Tyneside extended to the summer of 2028.
Guimaraes was one of Newcastle's first big buys when their Saudi Arabian-backed takeover was completed in the course of the 2021/2022 season.
The 25-year-old has since helped Eddie Howe's side avoid relegation, finish in the top four and are now competing impressively with Europe's elite in the Champions League.
Guimaraes has now made 67 appearances and scored 11 goals across all competitions for the Magpies.
Speaking to the club's official website, Guimaraes said: "I'm so happy here. It's a place that is so comfortable to be and I hope to keep making the supporters happy and helping the team do well. That's my goal, because there are no words to describe how happy I am to be here.
"I remember in my first interview, I said I wanted to play for this club in the Champions League and now it's happening. We are doing so well and when I look around the pitch at my team-mates, I am so proud of them all. I'm proud of everyone; the team, the staff, the owners and the fans."
Newcastle head coach Eddie Howe, who signed Guimaraes from Lyon in January 2022, said: "I'm delighted to get Bruno signed and committed to the long-term future of the football club. He's such an important player and he's done so well since he joined the club. He's been a huge success since he's been here so I just hope that he can continue in that vein and carry on his success with us.
"I think he epitomises the recent success we've had. He's put in so many good displays, he's very consistent and he's got a great personality off the pitch as well.
"He cares very deeply about Newcastle United and the success of the club and he's got a great relationship with our supporters. He's been a key signing for us - definitely the type of signing that we want to make."
