You may win the game diplomatically by convincing enough faction leaders to unite behind you as Supreme Leader of Planet. A 3/4 vote of the Planetary Council and the knowledge of Mind/Machine Interface is required to secure such election. Only the leader of one of the two factions with the highest vote totals may stand for election as Governor or Supreme Leader.
When a Supreme Leader is elected, a faction leader may choose to defy the will of the Council and refuse to submit. In this case, the Supreme Leader must, with the help of loyal factions, conquer all defiant factions to achieve a Conquest victory. Because of the military power usually required to secure election as Supreme Leader, defying the will of the Council is generally fairly suicidal. Other factions will therefore usually only take this course if you have committed atrocities against them or grossly and repeatedly betrayed them.
If you win a Diplomatic Victory, you are awarded 1200 points minus 2 for every game turn elapsed. If Cooperative Victory is enabled and your Pact Brother or Sister is elected Supreme Leader, you are awarded half this total.
No leader can win a diplomatic victory so long as any Progenitor faction remains unconquered.