In 2366, Duras was part of the Klingon High Council, when a Romulan ship was captured with new evidence that shed more light on the massacre at Khitomer. The records carried by the Romulan ship proved that Ja'rod, father of Duras, was the man who sent the Romulans the Khitomer outpost's shield codes, enabling the Romulans to lower the shields and kill nearly all the Klingons on the base. Fearing that labeling Duras as the son of a traitor as required by Klingon law would split the council and plunge the Klingon Empire into civil war, the council instead decided to alter records and blame Ja'Rod's rival Mogh for the Romulan attack.
When Mogh's son Worf discovered that his father had been judged guilty of the attack by the council, he and his brother Kurn returned to Qo'noS to challenge the council. With the assistance of the crew of the USS Enterprise-D, Worf and Kurn soon discovered the truth. The council was unwilling to reveal the truth. Worf decided to accept discommendation to keep the Empire from falling into civil war, but warned Duras that the truth would one day be revealed. (TNG episode: "Sins of the Father")
Some time after this confrontation with Worf, Duras began poisoning Chancellor K'mpec with Veridium Six. By early 2367, K'mpec was dying from the poison. When it became known that K'mpec was dying, Duras and Gowron emerged as the two strongest candidates to succeed K'mpec as Chancellor. K'mpec was not positive who was poisoning him, but believed it to be either Duras or Gowron. K'mpec met with, and managed to convince Starfleet Captain Jean-Luc Picard to become Arbiter of Succession upon his death. After K'mpec died, Duras attempted to assassinate Gowron by having his bodyguard detonate a Romulan explosive during the Sonchi ceremony.
In the following investigation, when Worf and Picard both voiced suspicions about Duras, Ambassador K'Ehleyr began investigating Duras, and uncovered the truth of the Khitomer massacre on her own. Duras confronted, and then killed K'Ehleyr. Discovering this, Worf claimed the Right of Vengeance, and entered into combat with Duras. Duras proved to be no match for Worf, and Worf drove his bat'leth into Duras' throat. The Empire considered this to be in accord with their laws and tradition, and closed the matter. Worf was reprimanded by Jean-Luc Picard for carrying out this killing. (TNG episode: "Reunion")