Sobhi joins on a three-year deal, staying in the Premier League after Stoke were relegated to the Championship following the 2017-18 season.
"I'm very happy that we will be able to welcome Ramadan to the club. He's a real talent and has achieved a lot for a player who is only 21 years old," Huddersfield boss David Wagner said in a club release.
"We're looking forward to working hard with Ramadan on the training pitch to give him every chance of success at Huddersfield Town."
Sobhi has been capped 26 times by Egypt, and is set to play a significant role in his country's first World Cup since 1990.