Perhaps, he was unable to pursue his career when Marcus Aurelius' son Commodus became emperor. Not everyone who had been trusted by the old man was a friend of the young man. However, Asellius was to occupy two very important offices at the end of Commodus' reign, which suggests that he was among his favorites, and this in turn suggests that he occupied an important but not very visible office in Rome - for example, one of the financial prefectures.
In c.188 Asellius was appointed as governor of Syria. This was not a sinecure, because this was a frontier province with two legions (III Gallica and IIII Scythica). There were no complaints about his tenure of office, and he was promoted to the governorship of Asia. Here, we find him in 193, when the emperor Pertinax was killed and civil war broke out between three men - Asellius' relative Clodius Albinus, the governor of Britain; the governor of Pannonia Superior Septimius Severus; and Pescennius Niger, Asellius' successor as governor of Syria.
At first he wanted to remain neutral, but he was forced to make a decision. Only six legions had refused to make a choice; the others favored Severus, who controlled twelve legions. He was by far the strongest candidate and was closest to Rome, which he captured in June. Then, he decided to attack Pescennius (who had nine legions) and marched to the east. Now, Asellius was forced to make a decision - either to side with Severus, which would give this man a stronghold in Asia Minor, or to side with Pescennius, which was the only way to help his relative, the weakest of the three pretenders (three legions). Asellius preferred the latter and was immediately sent to Cyzicus, on the southern shore of the Sea of Marmora, where he and a mixed corps of volunteers and legionaries would have to defend Asia and support Pescennius' European bulwark Byzantium, where his emperor briefly resided.He could not prevent, however, that Severus' soldiers landed at Cyzicus. The two armies fought a battle, Asellius was defeated, fled, and was killed. The army of his opponent could now break through Asia Minor and invade Syria. This they did, and Pescennius was defeated near Issus (March 194). Three years later, Severus also defeated Albinus. At Cyzicus, he had laid the foundation of his one-man rule.
Asellius Aemilianus is not to be confused with the A. Sellius who was executed by Septimius Severus.