Quintillus was born at Sirmium in Pannonia Inferior. Originating from a low-born family, he rose to prominence when his brother Claudius II Gothicus became emperor in 268. He may have been the Procurator of Sardinia during his brother's reign. He was acclaimed as emperor by his soldiers immediately following his brother's death, then confirmed by the Senate. However, the legions campaigning along the Danube were either unaware or disapproved of Quintillus' elevation. They instead elevated their general Aurelian as emperor. The few existing records disagree on the length of his reign, which is variously reported to have lasted as few as 17 days and as many as 177 days (about six months). Records also disagree on the cause of his death. Historia Augusta reports him murdered by his own soldiers in reaction to his strict military discipline. Jerome reports him killed, presumably in conflict with Aurelian. John of Antioch and Joannes Zonaras reported Quintillus to have committed suicide by opening his veins and bleeding himself to death. John reports the suicide to have been assisted by a physician. All records agree he died at Aquileia.