During the Cold War with the Galactic Republic, he and Lord Calaverous were investigating how did Lord Zash manage to be at a party and at the same time, assassinating Darth Skotia. He questions Zash's apprentice, Kallig, though Calaverous believed that it would be futile. Kallig claimed to have killed Skotia, though Calaverous believed the apprentice was not being truthful. As they departed Skotia's, now Zash's chambers, Kirnon tells Calaverous that Zash is growing too powerful too quickly, for no Sith has committed such brazen murder yet appeared to be in another place at the time, commenting that it's enough to wake the Sith Emperor.
After the start of the Galactic War, Kirnon was present on Corellia during the Kaggath between Lord Kallig and Darth Thanaton as a spectator during the challengers' supposedly final duel.
Kirnon journeyed to Dromund Kaas after Kallig finally defeated Thanaton and claimed his seat on the Dark Council, where other members of the Sphere of Ancient Knowledge pledged allegiance to the new Dark Lord of the Sith.
If Darth Achelon is killed, Kirnon will pledge allegiance to Kallig in his place.