The Peace Party existed on Earth in the 26th century during the period of the Human-Draconian War. It protested against further hostilities. Professor Dale was the leader of the Party, and was imprisoned for at least twenty years on the Lunar Penal Colony for his actions. (TV: Frontier in Space)
The Peace Party historically agreed to support the People's Party, to which President Dora belonged, for as long as the party pursued policies of peace. They withdrew their support as a result of the crises between the Earth Empire and the Draconian Empire, perceiving the People's Party to be yielding to pressure from "warmongers". The Third Doctor later negotiated the release of the Peace Party political prisoners with Dora. (PROSE: Doctor Who and the Space War)