Glasner has signed a deal with Forest after leaving Crystal Palace this summer after two seasons in charge at Selhurst Park.
The 51-year-old made a huge impact at Palace, winning the FA Cup, the FA Community Shield and the UEFA Conference League during his time at the club.
In a statement from Nottingham Forest, Glasner said: “I’m delighted to join Nottingham Forest as head coach. From my very first conversations with the owner and the leadership team, it was evident to me that they have a clear vision for this football club and complete trust and belief in me and my staff to build a strong future together over the long term.
“Nottingham Forest is a club with incredible prestige and history, a two-time European Champion with one of the most passionate fan bases in football. Our aim is to build a team that can help take the club to the next level in the years ahead and that our supporters can be proud of.
“My immediate focus is on meeting the players and staff and getting to work as we begin pre-season. I’m excited for the future and will work tirelessly to represent this great club with pride and to bring success on the pitch. I can’t wait to get started.”
Glasner succeeds manager Vitor Pereira after Forest triggered a mutual termination in the Portuguese's deal, which ran out on June 30.