The 25-year-old midfielder, the J League player of the year, will arrive at Parkhead from Yokohama F Marinos, initially on loan before making the move permanent after the end of the current season.
"I really am delighted to be joining Celtic, such a huge and successful club known across the world," the Japan international told Celtic's website on Friday. "I can't wait to begin my journey."
🆕✍️ #WelcomeTomoki— Celtic Football Club (@CelticFC) December 30, 2022
We are delighted to announce the signing of current J-League Player of the Year and Japanese international Tomoki Iwata.
Welcome to #CelticFC, Tomoki! 🍀🇯🇵