The dynasty was founded by Imad ed-Din Zengi, who became the Seljuk Atabeg (governor) of Mosul in 1127. He quickly became the chief Turkish potentate in Northern Syria and Iraq, taking Aleppo from the squabbling Ortoqid emirs in 1128, and capturing the County of Edessa from the Crusaders in 1144. This latter feat made Zengi a hero in the Muslim world, but he was assassinated by a slave two years later, in 1146.
On Zengi's death, his territories were divided, with Mosul and his lands in Iraq going to his eldest son Saif ad-Din Ghazi I, and Aleppo and Edessa falling to his second son, Nur ad-Din Mahmud. Nur ad-Din proved to be as competent as his father. In 1149 he defeated and killed Prince Raymond of Antioch in battle, and the next year conquered the remnants of the County of Edessa west of the Euphrates River. In 1154 he capped off these successes by his capture of Damascus from the Burid Emirs who ruled it.
Now ruling from Damascus, Nur ad-Din's success continued. Another Prince of Antioch, Raynald of Chatillon was captured, and the territories of that Principality greatly reduced. In the 1160s, Nur ad-Din's attention was mostly held by a competition with the King of Jerusalem, Amalric I, for control of the Fatimid Caliphate of Egypt. Ultimately, Nur ed-Din's Kurdish general Shirkuh was successful in conquering Egypt in 1169, but Shirkuh's nephew and successor as Governor of Egypt, Saladin, rejected Nur ad-Din's control.
Nur ad-Din was preparing to invade Egypt to bring Saladin under control when he unexpectedly died in 1174. His son and successor As-Salih Ismail al-Malik was only a child, and was forced to flee to Aleppo, which he ruled until 1181, when he was murdered and replaced by his relation, the Atabeg of Mosul. Saladin conquered Aleppo two years later, ending Zengid rule in Syria.
Zengid princes continued to rule in Northern Iraq well into the 13th Century, ruling Mosul until 1234 and with their rule not coming finally to an end until 1250.