The 20-year-old featured three times at this summer's World Cup as Ivory Coast reached the knockout stages, and arrives from Bundesliga side TSG Hoffenheim for an undisclosed fee.
Bazoumana becomes Newcastle's second senior arrival of the summer, after French goalkeeper Ewen Jaouen joined on Wednesday.
"I'm very, very happy to be here. It was my dream since I was young to play in the Premier League for a big team like Newcastle," Bazoumana said.
"Newcastle is like a family, which will help me show my best on the pitch. I will give my best every single day for this shirt.
"I'm very excited to join Newcastle and I can't wait to meet my team-mates, the supporters and everybody at the club. I'm also very excited to play at St. James' Park for the first time."
Manager Eddie Howe welcomed the signing.
"We're really pleased to have been able to bring Bazoumana to Newcastle United. He has shown his ability to perform in a top European league during his time in Germany and has gained really good experience with his national team, especially at this summer's World Cup," Howe said.
"We feel that he's a player with a really high ceiling - he's somebody who we believe can offer us something different. He also has a lot of potential to unlock and we're really looking forward to working with him."
Sporting director Ross Wilson welcomed the deal.
"We're delighted to welcome Bazoumana to Newcastle United. At just 20 years old, he's already a hugely exciting young talent who has progressed year on year," Wilson said.
"We are sure there's plenty more growth still to come - development we're excited to nurture here at Newcastle. We've been working to get this transfer arranged in recent weeks, whilst Bazoumana has been at the World Cup.
"Finally, I'd like to thank TSG Hoffenheim for their professionalism in all of our discussions and for the care they've shown him. I know they share our excitement in Bazoumana's quality and potential."
Bazoumana began his career at ASEC Mimosas, winning the league title in his debut season, before a move to Hammarby IF in Sweden in early 2024, where eight goals in 23 matches caught Hoffenheim's attention in February 2025.
He went on to make 45 appearances in all competitions during his season-and-a-half in Germany, scoring five goals and nine assists last season as Hoffenheim secured Europa League football with a fifth-place finish, before making his international debut in October 2025 and helping Ivory Coast reach the round of 32 at this summer's World Cup.