Origin and early career. L. Catilius Severus came from the eastern provinces — variously reconstructed as Apamea in Bithynia or as Antioch in Pisidia (the exact localisation remains a matter of dispute in the prosopographical literature; see Birley 2000 and PIR² C 558). The full polyonymous name — L. Catilius Severus Iulianus Claudius Reginus — reflects several generations of family adoptions and inheritances. This is the first generation in the family to reach the Roman consulate.

Career. Military tribune, quaestor, legate, proconsul of Asia Minor (probably). Suffect consul 110 under Trajan (with C. Erucianus Silo); ordinary consul 120 under Hadrian (with T. Aurelius Fulvus Boionius Arrius Antoninus — the future Antoninus Pius — characteristically: Severus took formally the senior place in the fasti of the year in which the future emperor was his colleague). Then the governorship of Syria Palaestina (probably in the early 130s) and the prefecture of the city (praefectus urbi) under Hadrian in the closing years of that reign. The office — the highest urban magistracy, presiding over the senatorial court, effectively head of the city's administration — was normally given to aging consulars of special standing.

The denouement at the succession of 138. At the critical moment of the adoptive transmissions of 138 (Hadrian → Antoninus Pius → Marcus), Catilius Severus, according to SHA Hadrian 24, found himself in opposition to the choice of Antoninus and was deprived of the prefecture of Rome — historians disagree as to whether this was his own frustrated claim to the succession or simply opposition to the adoption of Antoninus. His name then disappears from the sources; he died approximately at the same time (138/9), most likely in disgrace.

The connection to Marcus: marriage to Domitia Lucilla Maior. Severus's principal kin relationship to Marcus is through his marriage to Domitia Lucilla the Elder (Marcus's maternal grandmother). This was apparently her second marriage (the first to the father of Domitia Lucilla Minor, see below). Through this marriage Severus became the stepfather of Marcus's mother and, by the Roman family reckoning, Marcus's "great-grandfather" (proavus / προπάππος), although biologically he stood in no kinship at all to Marcus.

The adoptive connection was so formally weighty that Marcus's full childhood name included his cognomen: M. Annius Catilius Severus. The name Catilius Severus dropped out of Marcus's full names only after 138 — following the adoption by Hadrian-Antoninus and the disgrace of Catilius Severus.

• 01-04 — the only direct mention of Catilius Severus in Marcus; programmatic: the three principles of education.
• In 01-17 (the closing thanksgiving paragraph) Marcus gives thanks "that I had good relatives, good teachers"; the great-grandfather is not named specifically but is implicitly included.

• SHA Hadrian 5.10 and 24.5–8 — the two principal places: the first on Catilius Severus's early service under Hadrian, the second on his disgrace at the succession of 138.
• SHA Marcus 1.4–9 — biographical context for Marcus's early tutors (the name Catilius Severus as "great-grandfather" at 1.10).
• PIR² C 558 — the standard prosopographical entry.
• A. Birley, Marcus Aurelius: A Biography, rev. ed., Routledge, 2000, ch. 2 ("The Family"), especially pp. 31–35 — the reconstruction of the kin connection through Domitia Lucilla Maior.
• A. Birley, Hadrian: The Restless Emperor, Routledge, 1997 — for the context of the city prefecture under Hadrian and the crisis of 138.
• R. Syme, Tacitus, Oxford 1958, app. 65 and passim — the kin network of the Antonine elite, with mentions of Catilius Severus.
• W. Eck, Die Statthalter der germanischen Provinzen vom 1.–3. Jahrhundert, Köln 1985 — for the context of governorship careers of senators of Catilius Severus's generation.