The bout at the O2 in London, reportedly worth £10million, had hung in the balance after it emerged on Wednesday that Benn had failed a drugs test.
Joint promoters Matchroom and Wasserman insisted the fight would still go ahead as planned with the backing of both Benn and Eubank Jr despite it being prohibited by the British Boxing Board of Control (BBBofC).
The promoters sought an injunction in the High Court to have that overturned. That hearing was scheduled for Thursday afternoon but, amid concerns the decision might not come until late on Friday, the decision was made to pull the plug and postpone the fight.
Reports suggested that the adverse analytical finding for traces of the substance clomifene, usually a fertility drug for women, from a sample by the Voluntary Anti-Doping Agency (VADA) dated back to August.
The results of the sample it is understood were made public to the BBBofC on September 23 but the board waited until Wednesday to withdraw its sanctioning of the fight.
Matchroom boss Eddie Hearn had initially said he was confident the fight could go ahead under the auspices of the BBBofC but that he had no plans to seek a foreign governing body to sanction it if that bid was unsuccessful.
"After discussions with various parties, we have taken the decision to formally postpone the bout between Chris Eubank Jr. and Conor Benn,” said a joint statement from Matchroom and Wasserman on Thursday. “It is undeniable that the British Boxing Board of Control’s decision to withdraw their sanctioning was procedurally flawed and without due process. That remains a legal issue between the promoters and the board which we intend to pursue.
"However, whilst there are legal routes to facilitate the fight taking place as planned, we do not believe that it is in the fighters’ interests for those to be pursued at such a late stage, or in the wider interests of the sport. As promoters, we take our obligations and duties very seriously, and a full investigation will now need to take place. We will be making no further comment at this time and news for ticket holder refunds will follow."