Gowron becomes chancellor after the death of K’mpec.
In the TNG episode “Reunion,” K’mpec dies after being poisoned and asks Captain Jean-Luc Picard to oversee the Klingon rite of succession. The leading contenders are Gowron and Duras, two powerful Klingon nobles whose rivalry threatens to divide the Empire. Picard is appointed Arbiter of Succession and must determine which candidate can lawfully claim the chancellorship.
The succession becomes entangled with the earlier political disgrace of Worf’s family. Duras had helped frame Worf’s father, Mogh, for treason connected to the Romulan attack on Khitomer. When Duras murders K’Ehleyr after she discovers evidence against him, Worf invokes the Klingon right of vengeance and kills Duras in ritual combat.
With Duras eliminated, Gowron becomes chancellor. He later faces a challenge from Duras’s son, Toral, during the Klingon civil war. Worf and Kurn support Gowron, and Gowron eventually restores the honor of the House of Mogh. Martok becomes chancellor only much later, after Worf kills Gowron during the Dominion War.