The 20-year-old shot-stopper made 34 Ligue 2 appearances during the 2025/26 season, keeping 15 clean sheets, and has represented his country at Under-21 level.
Jaouen joined Reims in the summer of 2023 after beginning his professional career with Guingamp.
He spent the second half of the 2023/24 campaign on loan at Rodez, before moving to USL Dunkerque for the 2024/25 season where he was part of the squad that reached the semi-finals of the Coupe de France, losing to eventual winners Paris Saint-Germain.
On signing for the Magpies, Jaouen said: “I’m really excited to become a Newcastle United player.
“I’ve heard so much about the supporters and how they are the best in the country. The passion of the entire city and the atmosphere at St James’ Park are famous throughout football, and I can’t wait to experience that for myself and become a true Geordie.
“As a goalkeeper, I enjoy one on one situations and playing as a modern keeper, building from the back and being comfortable with the ball at my feet.
"Now I want to develop alongside the amazing players and staff here, enjoy my football, and prove my value on the pitch.”