He is famous for his Attic Nights, a commonplace book, or compilation of notes on grammar, philosophy, history, antiquarianism, and other subjects, preserving fragments of the works of many authors who might otherwise be unknown today.

Medieval manuscripts of the Noctes Atticae commonly gave the author's name in the form of "Agellius", which is used by Priscian; Lactantius, Servius and Saint Augustine had "A. Gellius" instead.

[2] Gellius studied rhetoric under Titus Castricius and Sulpicius Apollinaris; philosophy under Calvisius Taurus and Peregrinus Proteus; and enjoyed also the friendship and instruction of Favorinus, Herodes Atticus, and Fronto.

[5] He was appointed by the praetor to act as an umpire in civil causes, and much of the time which he would gladly have devoted to literary pursuits was consequently occupied by judicial duties.

The Attic Nights are valuable for the insight they afford into the nature of the society and pursuits of those times, and for its many excerpts from works of lost ancient authors.

[7] The earliest critical edition was by Ludovicus Carrio in 1585, published by Henricus Stephanus; however, the projected commentary fell victim to personal quarrels.