When Tacitus refers to Gaius Suetonius Paulinus by one name, he almost invariably uses "Suetonius" rather than "Paulinus", and this convention is used here. It should however be noted that many later sources prefer to use "Paulinus", as "Suetonius" is usually understood to refer to the historian.
Having been praetor, he went to Mauretania in 41 AD as legatus legionis to suppress a revolt. He was the first Roman to cross the Atlas Mountains, and Pliny the Elder quotes his description of the area in his Natural History.
In the year 41 AD Suetonius Paullinus, afterwards Consul, was the first of the Romans who led an army across Mount Atlas. At the end of a ten days' march he reached the summit,—which even in summer was covered with snow,—and from thence, after passing a desert of black sand and burnt rocks, he arrived at a river called Gerj...he then penetrated into the country of the Canarii and Perorsi, the former of whom inhabited a woody region abounding in elephants and serpents, and the latter were Ethiopians, not far distant from the Pharusii and the river Daras (modern river Senegal)
Gaius Suetonius with his expedition south of the Atlas mountains was one of the first European explorers of Saharan Africa.
In 59 he was appointed governor of Britain, replacing Quintus Veranius, who had died in office. He continued Veranius's policy of aggressively subduing the tribes of modern Wales, and was successful for his first two years in the post. His reputation as a general came to rival that of Gnaeus Domitius Corbulo. Two future governors served under him: Quintus Petillius Cerialis as legate of Legio IX Hispana, and Gnaeus Julius Agricola as a military tribune attached to II Augusta, but seconded to Suetonius's staff.
In 61 Suetonius made an assault on the island of Mona (Anglesey), a refuge for British fugitives and a stronghold of the druids. The tribes of the south-east took advantage of his absence and staged a revolt, led by queen Boudica of the Iceni. The colonia of Camulodunum (Colchester) was destroyed, its inhabitants tortured, raped, and slaughtered, and Petillius Cerialis's legion routed. Suetonius brought Mona to terms and marched along the Roman road of Watling Street to Londinium (London), the rebels' next target, but judged he did not have the numbers to defend the city and ordered it evacuated. The Britons duly destroyed it, the citizens of Londinium suffering the same fate as those of Camulodunum, and then did the same to Verulamium (St Albans).
Suetonius regrouped with the XIV Gemina, some detachments of the XX Valeria Victrix, and all available auxiliaries. The II Augusta, based at Exeter, was available, but its prefect, Poenius Postumus, declined to heed the call. Nonetheless, Suetonius was able to assemble a force of about ten thousand men. Heavily outnumbered (the Britons numbered 100,000 according to Tacitus, 230,000 according to Dio Cassius), the Romans stood their ground. The resulting Battle of Watling Street took place at an unidentified location in a defile with a wood behind him, probably in the West Midlands somewhere along Watling Street - High Cross in Leicestershire and Manduessedum near the modern day town of Atherstone in Warwickshire have been suggested - where Roman tactics and discipline triumphed over British numbers. The Britons' flight was impeded by the presence of their own families, whom they had stationed in a ring of wagons at the edge of the battlefield, and defeat turned into slaughter. Tacitus heard reports that almost eighty thousand Britons were killed, compared to only four hundred Romans. Boudica poisoned herself, and Postumus, having denied his men a share in the victory, fell on his sword.
Suetonius reinforced his army with legionaries and auxiliaries from Germania and conducted punitive operations against any remaining pockets of resistance, but this proved counterproductive. The new procurator, Gaius Julius Alpinus Classicianus, expressed concern to the Emperor Nero that Suetonius's activities would only lead to continued hostilities. An inquiry was set up under Nero's freedman, Polyclitus, and an excuse, that Suetonius had lost some ships, was found to relieve him of his command. He was replaced by the more conciliatory Publius Petronius Turpilianus.
Suetonius became consul ordinarius in 66. In 69, during the year of civil wars that followed the death of Nero (see Year of four emperors), he was one of Otho's senior generals and military advisors. He and Publius Marius Celsus defeated Aulus Caecina Alienus, one of Vitellius's generals, near Cremona, but Suetonius would not allow his men to follow up their advantage and was accused of treachery as a result. When Caecina joined his forces with those of Fabius Valens, Suetonius advised Otho not to risk a battle but was overruled, leading to Otho's decisive defeat at Bedriacum. Suetonius was captured by Vitellius and obtained a pardon by claiming that he had deliberately lost the battle for Otho, although this was almost certainly untrue. His eventual fate remains unknown.