His grandfather served in the war against Sertorius with Pompey, through whose influence he obtained Roman citizenship; hence the name Pompeius, adopted as a token of gratitude to his benefactor. His father served under Julius Caesar in the capacity of secretary and interpreter.
Trogus himself seems to have been a man of encyclopaedic knowledge. Following Aristotle and Theophrastus, he wrote books on the natural history of animals and plants, which were frequently quoted by Pliny the Elder.
His principal work was Historiae Philippicae in forty-four books, so called because the Macedonian empire founded by Philip is the central theme of the narrative. This was a general history of those parts of the world that came under the sway of Alexander and his successors. Trogus began with a legendary Ninus, founder of Nineveh, and ended at about the same point as Livy (AD 9). Justin wrote an epitome of Trogus' lost work, and a series of prologi or summaries of the books. The last event recorded by Justinus is the recovery of the Roman standards captured by the Parthians in 20 BC. Ethnographical and geographical digressions were such a feature of the work that it developed the unwarranted reputation of being a universal history, never Trogus' intention.
Trogus left untouched Roman history up to the time when Greece and the East came into contact with Rome, possibly because Livy had sufficiently treated it. The work was based upon the writings of Greek historians, such as Theopompus (whose Philippica may have suggested Trogus' subject), Ephorus, Timaeus, Polybius. Chiefly on the ground that such a work was beyond the powers of a Roman, it is generally agreed that Trogus did not gather together the information from the leading Greek historians for himself, but that it was already combined into a single book by some Greek (very probably Timagenes of Alexandria).
His idea of history was more severe and less rhetorical than that of Sallust and Livy, whom he blamed for putting elaborate speeches into the mouths of the characters of whom they wrote. Of his great work, we possess only the epitome by Justin, the prologi or summaries of the 44 books, and fragments quoted in Vopiscus, Jerome, Augustine and other writers. But even in its present mutilated state it is often an important authority for the ancient history of the East.