The 26-year-old left-footed centre-back has signed a three-year contract at the City Ground and becomes Steve Cooper’s fourth signing of this window.
Moussa Niakhaté has spent the last four seasons playing in the Bundesliga for Mainz, making 128 appearances in the league.
How will he fit in?
Niakhaté typically plays on the left side of a back three but can also play left-back. Of course, Scott McKenna plays on the left of the Nottingham Forest back three, so Steve Cooper may explore the idea of switching the pair between the left and the centre.
The 6 ft 3 defender was formidable on the left side of the back three for Mainz last season.
Niakhaté scored four goals from defence in 30 Bundesliga matches. The 26-year-old had 1.7 interceptions, 1.3 tackles, and 2.2 clearances per game last season. In addition, the defender won 1.9 aerial duels per game, with a 70% success rate, and kept eight clean sheets.
Niakhaté also made 36 passes per game in the Bundesliga last season with a pass accuracy of 79%.
The defender was named Mainz captain ahead of the 2021/22 season and has been hailed an “unbelievable defender” by the official website of the Bundesliga.
How will Niakhaté fare in the Premier League?
Niakhaté has played against elite footballers in the German top flight for four seasons now.
In April, the defender captained his team to a 3-1 victory over a Bayern Munich side, which featured Robert Lewandowski, Serge Gnabry, Joshua Kimmich, and Alphonso Davies, among others. That game ended with Niakhaté scoring.
Niakhaté also tested himself against Premier League opposition during pre-season against Liverpool.
The defender was up against Mo Salah for the 46 minutes they both played during the friendly as they were both substituted at half-time when the game remained 0-0.
“It's true that we went up against each other a lot during the game. But I wanted to show what I was capable of against big players like Mo Salah," Niakhaté told bundesliga.com.
Signing a player of this calibre is the type of astute business we've come to expect from Forest during this window, and the Reds will be relieved to have added another Premier League signing to the squad.
Upon signing for Forest, Niakhaté told the clubs media team: "For me, this a dream to come to England and to sign for such a historic club in Nottingham Forest. The club is well known around the world and its fans are incredible.
“The Premier League is also the best league in the world and every player wants to play here.
"I’m just so excited to get started in pre-season, meet my new teammates and get ready for the new season, wearing the Garibaldi red and white at the City Ground.”