His most important work is the Institutiones Divinae ("The Divine Institutes"), an apologetic treatise intended to establish the reasonableness and truth of Christianity to pagan critics.

At the request of the Roman emperor Diocletian, he became an official professor of rhetoric in Nicomedia; the voyage from Africa is described in his poem Hodoeporicum (now lost).

[8] There, he associated in the imperial circle with the administrator and polemicist Sossianus Hierocles and the Neoplatonic philosopher Porphyry; he first met Constantine, and Galerius, whom he cast as villain in the persecutions.

Saint Jerome praised his writing style while faulting his ability as a Christian apologist, saying: "Lactantius has a flow of eloquence worthy of Tully: would that he had been as ready to teach our doctrines as to pull down those of others!

He wrote apologetic works explaining Christianity in terms that would be palatable to educated people who still practiced the traditional religions of the Empire.

"I relate all those things on the authority of well-informed persons, and I thought it proper to commit them to writing exactly as they happened, lest the memory of events so important should perish, and lest any future historian of the persecutors should corrupt the truth.

His works were copied in manuscript several times in the 15th century and were first printed in 1465 by the Germans Arnold Pannartz and Konrad Sweynheim at the Abbey of Subiaco.