Chairman Nigel Doughty told the club's official site: "It's always regrettable when it comes to making decisions like this one but we feel that some action had to be taken.
"It's not a decision that has been made in haste. We feel we have given Paul every chance to try and turn things around but, for one reason or another, the improvement we have all been desperate to see has not been forthcoming.
"We have 17 League games remaining this season and it is imperative that we do everything possible to improve results and stabilise our League position.
"We will be looking to appoint a manager as soon as possible in order to move the club in a forward direction once more."
He had been at the helm for two-and-a-half years after taking over from David Platt and was held in very high regard by the majority of all Forest fans.
"Paul Hart's Red and White Army" was still being sung by the Forest faithful during their 1-0 defeat at home to Coventry.
Former Forest defender Kenny Burns believes a lot of blame has to be put on the players and feels sorry for the man who has built Forest up again from scratch.
He told Sporting Life: "This will have hurt Paul Hart deeply. He'll be hurt and disappointed and I don't think it would be advisable for anyone to go near him for the next few days because he's liable to rip their head off.
"At the end of the day, it comes down to the players who have not really being doing their job on the pitch, they're the ones who have got to take a measure of responsibility for what's happened."
His sacking has promted rumours of Leeds United wanting his services but the Elland Road club have ruled-out a move for the 50-year-old.
Personally I would like to thank Paul for his hard work during his spell as Youth Academy director and Forest manager and wish him luck for the future.