As might be expected in the case of an army for which relatively little documentary evidence survives, it is possible to reconstruct the Seleucid military hierarchy only in its upper ranks, going no lower than the commanders of the independent contingents. Nothing apart from their ranks (which presumably were equivalent to those used in other Hellenistic armies) is known about officers of lower grades; no data are available on their identity, descent, nationality, and system of promotion. This is in contrast to the relatively abundant information on the Ptolemaic army supplied by Ptolemaic documents. Nevertheless, the little we do know about the cadre of the high-ranking commanders may contribute to our understanding of the reasons for the superiority of the Seleucid military organization over the Ptolemaic system.

The supreme command in the main campaigns was usually held by the king himself: Seleucus I at Ipsus, Cyrrhestica, and Curupedion; Antiochus I against the Galatians; Antiochus III against Molon, in the Fourth Syrian War (Seleucia, Porphyrion, Rabatamana, Raphia), against Achaeus (Sardis), in the expedition to the upper satrapies, in the Fifth Syrian War (Gaza, Panion), and in the Roman war (Thermopylae and Magnesia); Antiochus IV in his expeditions to Egypt and to the east; Demetrius I against Alexander Balas and Antiochus VII Sidetes in his campaign against the Parthians. In exceptional cases, when the terrain prevented him from fighting among his cavalry Guard, we find the king content to direct operations from behind the front line, or on its periphery, as at Porphyrion, Seleucia, Rabatamana, Sardis, and the Elburz.