Throughout his long career of 50 years, Poggio served a total of seven popes: Boniface IX (1389–1404), Innocent VII (1404–1406), Gregory XII (1406–1415), Antipope John XXIII (1410–1415), Martin V (1417–1431), Eugenius IV (1431–1447), and Nicholas V (1447−1455).

While he held his office in the Curia through that momentous period, which saw the Councils of Constance (1414–1418), in the train of Pope John XXIII, and of Basel (1431–1449), and the final restoration of the papacy under Nicholas V (1447), he was never attracted to the ecclesiastical life (and the lure of its potential riches).

After Martin V was elected as the new pope in November 1417, Poggio, although not holding any office, accompanied his court to Mantua in late 1418, but, once there, decided to accept the invitation of Henry, Cardinal Beaufort, bishop of Winchester, to go to England.

[7] In December 1435, at age 56, tired of the unstable character of his single life, Poggio left his long-term mistress and delegitimized the fourteen children he had had with her, scoured Florence for a wife, and married a girl of a noble Florentine family, not yet 18, Selvaggia dei Buondelmonti.

William Shepherd, author of Poggio's most extensive biography, finely comments on Valla's advantage in the literary dispute: the power of irony and satire (making a sharp imprint on memory) versus the ploddingly heavy dissertation (that is quickly forgotten).

After the death in April 1453 of his intimate friend Carlo Aretino, who had been the Chancellor of the Florentine Republic, the choice of his replacement, mostly dictated by Cosimo de' Medici, fell upon Poggio.

Poggio's declining days were spent in the discharge of his prestigious Florentine office—glamorous at first, but soon turned irksome—conducting his intense quarrel with Lorenzo Valla, editing his correspondence for publication, and in the composition of his history of Florence.

After July 1415—Antipope John XXIII had been deposed by the Council of Constance and the Roman Pope Gregory XII had abdicated—the papal office remained vacant for two years, which gave Poggio some leisure time in 1416/17 for his pursuit of manuscript hunting.

(p. 66) Poggio was marked by the passion of his teachers for books and writing, inspired by the first generation of Italian humanists centered around Francesco Petrarch (1304–1374), who had revived interest in the forgotten masterpieces of Livy and Cicero, Giovanni Boccaccio (1313–1375) and Coluccio Salutati (1331–1406).

[11] The literary passions of the learned Italians in the new Humanist Movement, which were to influence the future course of both Renaissance and Reformation, were epitomized in the activities and pursuits of this self-made man, who rose from the lowly position of scribe in the Roman Curia to the privileged role of apostolic secretary.

He became devoted to the revival of classical studies amid conflicts of popes and antipopes, cardinals and councils, in all of which he played an official part as first-row witness, chronicler and (often unsolicited) critic and adviser.

The treasures he brought to light at Reichenau, Weingarten, and above all St. Gall, retrieved from the dust and abandon many lost masterpieces of Latin literature, and supplied scholars and students with the texts of authors whose works had hitherto been accessible only in fragmented or mutilated copies.

[18][19][20] Poggio cultivated and maintained throughout his life close friendships with some of the most important learned men of the age: Niccolò de' Niccoli (the inventor of the italic script), Leonardo Bruni ("Leonardo Aretino"), Lorenzo and Cosimo de' Medici, Carlo Marsuppini ("Carlo Aretino"), Guarino Veronese, Ambrogio Traversari, Francesco Barbaro, Francesco Accolti, Feltrino Boiardo, Lionello d'Este (who became Marquis of Ferrara, 1441–1450), and many others, who all shared his passion for retrieving the manuscripts and art of the ancient Greco-Roman world.

These learned men were adept at maintaining an extended network of personal relations among a circle of talented and energetic scholars in which constant communication was secured by an immense traffic of epistolary exchanges.

Poggio, like Aeneas Sylvius Piccolomini (who became Pius II), was a great traveller, and wherever he went he brought enlightened powers of observation trained in liberal studies to bear upon the manners of the countries he visited.

We owe to his pen curious remarks on English and Swiss customs, valuable notes on the remains of ancient monuments in Rome, and a singularly striking portrait of Jerome of Prague as he appeared before the judges who condemned him to the stake.

[11] In literature he embraced the whole sphere of contemporary studies, and distinguished himself as an orator, a writer of rhetorical treatises, a panegyrist of the dead, a passionate impugner of the living, a sarcastic polemist, a translator from the Greek, an epistolographer and grave historian and a facetious compiler of fabliaux in Latin.

[11] His cultural/social/moral essays covered a wide range of subjects concerning the interests and values of his time: These compositions, all written in Latin − and reviving the classical form of dialogues, between himself and learned friends[23] − belonged to a genre of socratic reflections which, since Petrarch set the fashion, was highly praised by Italian men of letters and made Poggio famous throughout Italy.

Poggio's beautiful rhetorical prose turns his Historia Florentina into a vivid narrative, with a sweeping sense of movement, and a sharp portrayal of the main characters, but it also exemplifies the limitations of the newly emerging historical style, which, in the work of Leonardo Bruni, Carlo Marsuppini and Pietro Bembo, retained "romantic" aspects and did not reach yet the weight of objectivity later expected by the school of modern historians (especially since 1950).

In addition Poggio's works included his Epistolae, a collection of his letters, a most insightful witness of his remarkable age, in which he gave full play to his talent as chronicler of events, to his wide range or interests, and to his most acerbic critical sense.

Poggio was a fluent and copious writer in Latin, admired for his classical style inspired from Cicero, if not fully reaching the elegance of his model, but outstanding by the standards of his age.

Rising to a degree of elegance, to be sought for in vain in the rugged Latinity of Petrarca and Coluccio Salutati..."[25] His knowledge of the ancient authors was wide, his taste encompassed all genres, and his erudition was as good as the limited libraries of the time allowed, when books were extremely rare and extraordinarily expensive.

Among contemporaries he passed for one of the most formidable polemical or gladiatorial rhetoricians; and a considerable section of his extant works is occupied by a brilliant display of his sarcastic wit and his unlimited inventiveness in "invectives".

Invectivae ("Invectives") were a specialized literary genre used during the Italian Renaissance, tirades of exaggerated obloquy aimed at insulting and degrading an opponent beyond the bounds of any common decency.

Poggio's most famous "Invectives" were those he composed in his literary quarrels, such as with George of Trebizond, Bartolomeo Facio, and Antonio Beccadelli, the author of a scandalous Hermaphroditus, inspired by the unfettered eroticism of Catullus and Martial.

All the resources of Poggio's rich vocabulary of the most scurrilous Latin were employed to stain the character of his target; every imaginable crime was imputed to him, and the most outrageous accusations proffered, without any regard to plausibility.