Itūr-Mēr was the tutelary god of Mari, an ancient Mesopotamian city identified with the modern site of Tell Hariri in Syria, located close to the border with Iraq. He is first attested in documents from the šakkanakku period, roughly contemporary with the Third Dynasty of Ur. His importance outside Mari itself was minor. According to Ichiro Nakata it is possible he was initially worshiped in Idamaraz, and was later introduced to Suprum as well under either Yaggid-Lim or Yahdun-Lim. Multiple documents indicate that a temple dedicated to Itūr-Mēr existed in Mari. According to Cinzia Papi, depending on the interpretation of the so-called "Temple of the Lions" it is possible that a shrine dedicated to him has been excavated, though it has also been suggested that belonged to Dagan instead. Textual references to shrines might refer to locations within the royal palace, rather than to separate religious structures.
After conquering Mari, Shamshi-Adad dedicated a throne to Itūr-Mēr and in an accompanying inscription credited him for granting him the right to rule it. It has been noted that this text is unusual as it does not mention Dagan in any capacity, even though he was usually invoked in earlier periods by newly established rulers of western parts of Mesopotamia, and the local god instead occurs alongside Enlil and Ashur.
During the reign of Zimri-Lim, among the known members of clergy responsible for the rites of Itūr-Mēr were a šangû (a priest; attested in a letter of Addu-dūrī, the queen mother) and a muḫḫûm (translated as "prophet;" the single known holder of this office bore the name Ea-maṣi). Despite the existence of the latter, no prophetic messages attributed to Itūr-Mēr are known from the Mari corpus. Multiple references to laborers working in fields belonging to the temple of Itūr-Mēr are known too. They were presumably responsible for harvesting barley which in turn was supplied to the temple personnel.
The number of offerings to Itūr-Mēr mentioned in known documents indicates that he was one of the main deities of the pantheon of Mari. He was celebrated during a festival taking place on the twenty seventh day of the month Lilliātum in the local calendar. He received six sheep during it, the same number as other major deities, Addu, Annunitum, Belet Ekallim, Dagan, Ea, Nergal, Ninhursag (possibly to be understood as a stand-in for Dagan's wife Shalash in texts from Mari) and Shamash. Another document mentions the delivery of a small amount of gold to a certain Mukannišum so that he could fashion a necklace for Itūr-Mēr for a festival referred to as inūma zāmirī. Preparations of a palanquin are also mentioned in one of the administrative documents. It was apparently richly decorated, as the instructions mention that 6 pounds of gold were provided to fashion inlays including “1 Dagan figure, 1 royal figure, 1 Yakrub-El figure, 3 figures of mountain (gods), and diverse locals that face the chest; 2 uridu-genies and 2 lamassatum-genies; 1 middle mountain; 2 [...]. and 2 forelocks for the chest.”
Itūr-Mēr is well attested in theophoric names from Old Babylonian Mari. Examples include Ana-Itūr-Mēr-taklāku ("I trust in Itūr-Mēr"), Ḫatnī-Itūr-Mēr ("Itūr-Mēr is my male relative"), Ḫanna-Itūr-Mēr ("Itūr-Mēr is gracious"), Ipqu-Itūr-Mēr ("Itūr-Mēr is protection"), Itūr-Mēr-gamil ("Itūr-Mēr is merciful"), Itūr-Mēr-ḫīnāya ("Itūr-Mēr is the two eyes [possibly: of the country]"), Itūr-Mēr-šamaḫ ("Itūr-Mēr listens"), Itūr-Mēr-tillātī ("Itūr-Mēr is my ally"), and Itūr-Mēr-ḫiṣra (meaning unknown).
After Mari was destroyed by Hammurabi, Itūr-Mēr continued to be worshiped in the kingdom of Ḫana, whose main urban center was likely Terqa, through the rest of the Old Babylonian period. Since even during the reign of Zimri-Lim he was not worshiped in Terqa, Ichiro Nakata proposes that he might have been introduced there by former members of the Mariote administration who fled there after the city was sacked by Babylonians. Paul-Alain Beaulieu instead considers the presence of Itūr-Mēr in texts from Terqa to possibly indicate that Mari was not entirely abandoned in this period. Charpin especially uses the continued invocation of Itur-Mer in oaths from the kingdom of Hana to argue that Mari continued to function as a capital of the kingdom. Nakata additionally assumes that the disappearance of Yakrub-El from the local pantheon of Terqa was the result of introduction of Itūr-Mēr. One of the Ḫana texts mentions a house belonging to Itūr-Mēr, though he shared its nominal ownership with Dagan, Shamash and the local ruler, Išar-Lim. Kings of Ḫana continued to mention Itūr-Mēr in their documents as late as during the reign of Mitanni king Parattarna. A text from Ugarit that mentions “the great gods of the land of Mari” lists Addu, Dagan, and a third deity whose name is uncertain. One of the suggestions for the reading of the name is Utul-Miri (shepherd of the land of Mari) which could then possibly be a late interpretation of Itur-Mer.