The Freethinkers were a political party that during the Star Imperium favored a creation of an intergalactic republic and abolition of the monarchy of the Imperial Sovereign. After the rise of the United Planets in Year 13,100, the Freethinkers became a secular party that opposed the mixing of religion and politics.

The Freethinkers first emerged after Satei IVs short reign as Sovereign (Year 2134 to 2137). By Year 2150, there were the first signs of a Freethinker party in Parliament. In that year, it was just a small handful of mostly Aliens, but gradually, it gained support among Star Elves and Asguardian Dwarfs.

By Year 2350, between 25 percent and 40 percent of the Parliament's Archons and Honored Aliens were aligned with the Freethinkers, and in Year 2356 the Blue Monarchists, Red Monarchists, and Moderate Party formed the loose coalition called the Monarchist Party to counter the ideological threat of the Freethinkers. Until the last century of the Star Imperium, the Monarchist Party retained the support of 60 percent to 75 percent of the parliamentary membership. Nevertheless, the Monarchists remained often seriously divided thanks to the Blue Monarchists and the Red Monarchists, often making it impossible to elect an Imperial Sovereign, with the position of Sovereign vacant for centuries at a time. By the time of the United Planets, many historians noted that very often the extreme difficulty in electing a Sovereign led to the powers of the Sovereign being exercised by the Council of Twelve via it's regency powers, leading them to sometimes call the Star Imperium a De Facto Intergalactic Republic. This was thanks to the Freethinkers party.

Freethinkers during the United Planets were mostly an opposition party, though on rare occasions they would form a coalition in the Council of Ministers with the Incarnate Party.

Freethinkers, along with some members of the Monarchist Party, spearedheaded the creation of Stellar sectors, Subsectors, and sector and Subsector assemblies.