Orta was born on Bajor and was orphaned as an infant. He was raised by his foster parents, Gan Marta and Gan Treo and was known as Gan Orta. His foster parents collaborated with the Cardassians who were occupying Bajor at the time. When Orta was ten, both foster parents were executed by the Cardassians for providing aid to Bajoran refugees. He then stowed away on a Ferengi freighter, and traveled to the Bajoran refugee camp on Valo II. From this point on, he used only the name Orta.
On Valo II, Orta met Tova Syed, who would become a lifelong friend and loyal associate. Both joined an anti-Cardassian terrorist cell, striking at a number of Cardassian worlds. Over the next twenty years, Orta became one of the most infamous Bajoran terrorists, to the point where any off-world act against the Cardassians was attributed to him.
In his thirtieth year, Orta was betrayed by a Yridian weapons dealer, captured by the Cardassians, and returned to Bajor as a prisoner. En route, a Cardassian glinn burned his face with acid, and once on Bajor, an Obsidian Order interrogator cut out his vocal cords. He was then to be turned over to Gul Madred for further interrogation, but was then rescued by Tova Syed and fellow members of his resistance cell. Orta did succeed, however, in murdering the Obsidian Order agent before leaving Bajor. (DS9 - The Brave and the Bold, Book One novella: The Second Artifact)
Though scarred, Orta was still able to rally his followers. However, his supply lines were severely curtailed by the Cardassians, to the point where his cell could no longer maintain warp-speed ships, and were restricted to the Valo system. (TNG episode: "Ensign Ro")
In 2370, two years after the end of the Cardassian Occupation, he agreed to return to the Bajoran system, purportedly to farm Bajor's newly arable second moon. In actuality, he had hoped to spark a new war between Bajor and the Federation, using Akwar's Ninth Prophecy as a pretext. Orta's plans were aided when he discovered the second of the four Malkus Artifacts, which acted as a powerful energy weapon. After killing Commander Rodzinski of the USS Odyssey and Orta's own friend Tova Syed, he took Captain Declan Keogh, Major Kira Nerys and Lieutenant Jadzia Dax hostage. He attempted to tie the Artifact into the weapons array of the Starfleet runabout USS Rio Grande, but was foiled by an anti-Maquis protocols programmed into the vessel's systems.