In late 2376, he was charged by Chancellor Martok to investigate the events leading to the abortive challenge between Rodek and Klag, and he uncovered the evidence of Dorrek's dishonorable actions. (KE novel: A Burning House)
In 2379, Worf had a meeting with the Council regarding the upcoming election for Federation President. Grevaq attempted to ask Worf if the Federation was responsible for replacing Emperor Kahless with a hologram, but he was chastised by Martok for attempting to speak for him.
Some time soon after this, Alexander Rozhenko, acting on behalf of the Federation, met with Grevaq and was able to convince him to pledge his continued support for the Klingon-Federation alliance. (TNG novel: A Time for War, A Time for Peace)
Despite Grevaq's political leanings, when the High Council was confronted with sensor readings of the USS Ranger sacrificing itself for the planet Khitomer against the invading Borg Collective in 2381, he pledged support in the conflict against the Borg. (ST - Destiny novel: Gods of Night)