The brother of Demetrius II, Antiochus was elevated after Demetrius' capture by the Parthians. He married Cleopatra Thea, who had been the wife of Demetrius. Their offspring was Antiochus IX, who thus became both half-brother and cousin to Seleucus V and Antiochus VIII.
Sidetes defeated the usurper Tryphon at Dora and laid siege to Jerusalem in 134. According to Josephus the Hasmonean king John Hyrcanus opened King David's sepulchre and removed three thousand talents, which he then paid Antiochus to spare the city. Sidetes then attacked the Parthians, supported by a body of Jews under Hyrcanus, and briefly took back Mesopotamia, Babylonia and Media before being ambushed and killed by Phraates II. His brother Demetrius II had by then been released, but the Seleucid realm was now restricted to Syria.