The United Nations Transitional Authority (UNTA) was the international political body that dealt with all matters pertaining to human activities on Mars following the First Martian Revolution of 2061, taking over the activities of the UN Office for Martian Affairs. Officially, the UNTA was part of the UN; unofficially, it was a regulating authority entirely controlled by the private interests of the transnationals and later the metanationals. Presidency of UNTA rotated among its members.

In the 2080s-2090s, the presidency went Phyllis Boyle. She oversaw the construction of the second space elevator on Mars to replace the first one that had been destroyed during the revolution.

The UNTA approved of many terraforming giga-projects financed by metanationals. Under the UNTA were constructed the soletta and the solar lens. Entire canyons were also tented and genetically engineered organisms were massively released all around Mars.

With Martian economic activities recovering, the UNTA and the metanationals worried little about the Martian underground, which they suspected existed but did not know where. As the underground and the demimonde became more organized and started influencing great shares of the Martian population and the incoming Terran immigrants through such organizations as Free Mars, the UNTA and the metanationals made it a point to eradicate them. Metanationals security increased the ranks of the UNTA police troops and in the first two decades of the 22nd century they persecuted and destroyed all underground settlements around the South pole, among them Gamete. Sabishii was also burned extensively. Martial law with UNTA troops was established in several cities.

When the Second Martian Revolution finally broke out in 2127, Derek Hastings was the head of UNTA. The UNTA and the metanational forces were overwhelmed by the popular response to the revolution and the organized manner in which the revolutionaries went about neutralizing their offensive capabilities. Hastings retrieved to New Clarke with a group of UNTA officials and security and was forced to retaliate by force when the Kakaze attempted to take down the space elevator cable.

In 2128, the UNTA under Hastings was given a seat in the Pavonis Mons Congress that drafted the Martian constitution. The Martian government allowed the UNTA to keep a presence in Sheffield and manage immigration from Terra in terms agreed upon by both parties.