The former Northern Ireland international enjoyed a 10-year spell with the East Midlands outfit, during the most successful time in Forest’s history.
O'Neill helped them win the First Division title, two European Cups and two League Cups as a player and now the experienced manager has the opportunity to try and take his beloved club back to the big time.
Forest parted company with Aitor Karanka last week and have moved swiftly to bring in O'Neill, with the club currently just four points off the playoffs.
The length of O'Neill's contract at present has not been confirmed by the Championship side, who lost 2-0 to strugglers Reading in their last league outing on 5th January, before being knocked out of the FA Cup at the hands of Premier League giants Chelsea.
Forest will begin life with O'Neill at the helm on Saturday when they welcome Bristol City to the City Ground.
Nottingham Forest are 13/10 to win, 12/5 to draw and 2/1 to lose to the Robins.
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