“He’s a young player who’s already gained plenty of experience at club level, while his impressive performances last season also saw him gain his first caps for Sweden.”
Nygren told Celtic TV that “I feel amazing” after completing his transfer.
“I’m a very competitive person and this is something that I love about Celtic,” he said. “It’s a huge club and I love that – and also the winning mentality.
“I want to be with similar-minded people who also love to win.”
Asked what fans can expect from him, the Swede added: “I’m a player who wants to create a lot of chances and go towards goal.
“I’m a link between the defence and the offence and I can run a lot. I’m an offensive-minded player, but I also work hard and try to do my best in all parts of the game.
“I had my breakthrough when I was very young, so even though I’m 23 years old, I have played over 200 games. I have a lot of experience and that’s what I want to bring.”
Nygren leaves Nordsjaelland as the fourth-highest scoring player in their history after just three-and-a-half seasons with the side he helped finish fifth in the Danish Superleague last season.
“I came to FC Nordsjælland as a young boy and now I am leaving the club as a grown man,” he told the club website. “It has been a fantastic time for me.
“It has been important for me to play regularly and get big challenges both in the Superliga and in the Conference League. I was proud to wear the captain’s armband in many of the games this spring.”
Football director Alexander Riget said Nygren was moving on “by mutual agreement”.
“Benjamin Nygren is a really good example of what we can do as a football club,” he said.
“He came to FC Nordsjaelland as a 20-year-old talent who needed to find himself and now he is moving on in his career after having gone through a strong development where he has most recently established himself as a Swedish A-national team player.”