The Blues opted to make the change following yesterday’s Papa John’s Trophy final defeat to Salford on penalties.
It was another awful Pompey performance which finally forced the hand of owners Tornante, having previously pledged to stick by their manager for the duration of his contract.
At this moment in time it is unclear whether Jackett’s departure is by mutual consent or entirely initiated by the manager or club’s hierarchy.
Nonetheless, he leaves after almost four years at Fratton Park, having arrived in June 2017.
During that time he has led the Blues to two play-off semi-finals, the Checktrade Trophy and the Papa John’s Trophy final.
However, crucially, he has failed to win promotion and the vast majority of fans have been long calling for his dismissal.
The players have this morning been informed of matters at the training ground, with no caretaker yet announced.
Pompey travel to Peterborough on Tuesday night, having dropped to seventh in League One.