Nottingham Forest say club legend Martin O’Neill is “realising a lifelong dream” after he was appointed as manager of the Championship club.
The 66-year-old, who played 371 games and helped Forest win back-to-back European Cups, left his role as Republic of Ireland boss in November.
Forest are ninth in the table, four points outside the play-off places.
O’Neill has succeeded Aitor Karanka at the City Ground and is Nottingham Forest’s 11th manager since June 2011.
The length of the former Celtic, Aston Villa and Leicester manager’s contract has not been disclosed.
He guided the Republic of Ireland to the last 16 of the 2016 European Championships during his five years in charge.
Karanka’s exit from the City Ground – with Forest still very much in the promotion race – means O’Neill arrives in a strong position both on the field and off it.
After finishing 17th in 2017-18, they invested heavily during the summer, with Joao Carvalho arriving from Benfica for a club record fee of £13.2m and striker Lewis Grabban joining in a £6m deal from Bournemouth.
The Forest job is the Northern Irishman’s first return to club management since a mixed spell with Sunderland, which saw him guide the Black Cats away from relegation from the Premier League in his first season but then struggle again the following campaign prior to his sacking in March 2013.