The exact details of his birth are uncertain. He was almost certainly a bastard, the son of a Florentine banker and an unknown woman. An early biographer claimed his mother was a Parisien and that the city was also the place of his birth, this has been largely depreciated as a romanticism and his place of birth is more likely to have been in Tuscany, perhaps in Certaldo, the town of his father.
Boccaccio grew up in Florence. His father was working for the Compagnia dei Bardi and in the 1320s married Margherita del Mardoli, of an illustrious family. It is believed Boccaccio was tutored by Giovanni Mazzuoli and received from him an early introduction to the works of Dante. Around 1327 Boccaccio moved to Naples when his father was appointed to head the Neopolitan branch of his bank, Boccaccio was apprenticed to the bank and spent six years there. It was a trade for which he had no affinity and he eventually persuaded his father to let him study law at the Studium in the city. However, his father had introduced him into the Neopolitan nobility and the French-influenced court of Robert the Wise. Boccaccio had become a friend of fellow-Florentine Nicola Acciaiuoli and benefitted from his influence as lover of Catherine of Valois, later counsellor to Queen Joanna and the "Grand Seneschal".
It seems Boccaccio enjoyed law no more than banking but his studies allowed him the opportunity to study widely and make good contacts with fellow scholars. His early influences included Paolo da Perugia (a curator and author of a collection of myths, the Collectiones), the humanists Barbato da Sulmona and Giovanni Barrili, and the theologian Dionigi da San Sepolcro. In the 1330s Boccaccio also became a father, two illegitimate children of his were born in this time, Mario and Giulio.
In Naples Boccaccio began what he considered his true vocation, poetry. Works produced in this period include Filostrato (the source for Chaucer's Troilus and Criseyde), Teseida (ditto the Knight's Tale), Filocolo a prose version of an existing French romance, and La caccia di Diana a poem in octave rhyme listing Neopolitan women.
Boccaccio returned to Florence in early 1341, avoiding the plague in that city of 1340 but also missing the visit of Petrarch to Naples in 1341. He had left Naples due to tensions between the Angevin king and Florence, his father had returned to Florence in 1338 and bankruptcy and the death of his wife a little later. Although dis-satisfied with his return to Florence Boccaccio continued to work, producing Comedia delle ninfe fiorentine (also known as Ameto) a mix of prose and poems in 1341, completing the fifty canto allegorical poem Amorosa visione in 1342, Fiammetta in 1343 and probably the pastoral piece Ninfale fiesolano dates from this time. In 1343 time Boccaccio's father re-married, to Bice del Bostichi. His children by his first marriage had all died and he was gladdened by the birth of a son, Iacopo, in 1344. Boccaccio also became a father again, another illegitimate child, Violante, was born in Ravenna.
In Florence the overthrow of Walter of Brienne brought about the government popolo minuto. It diminished the influence of the nobility and the wealthier merchant classes and assisted in the relative decline of Florence. The city was further hurt in 1348 by the Black Death, later used in the Decameron, which killed maybe three-quarters of the city's population. From 1347 Boccaccio was spending much time in Ravenna, seeking new patronage, and despite his claims it is not certain he was actually present in plague-ravaged Florence. His step-mother died during the epidemic and his father, as Minister of Supply in the city was closely associated with the government efforts. His father died in 1349 and as head of the family Boccaccio was forced into a more active role.
Boccaccio began work on the Decameron around 1349. It is probable that the structure of many of the tales dates from earlier in his career, but the choice of a hundred tales and the frame-story lieta brigata of three men and seven women dates from this time. The work was largely complete by 1352 and it was Boccaccio's final effort in literature and one of his last works in Italian, the only other substantial work was the misogynist Corbaccio (dated to either 1355 or 1365). Boccaccio revised and rewrote the Decameron in 1370-71, this manuscript has survived to the present day.
From 1350 Boccaccio was less of a scholar, closely involved with Italian humanism and also with the Florentine government. His first official mission was to Romagna in late 1350, he revisited that city-state twice and was also sent to Brandenburg, Milan and Avignon. He also pushed for the study of Greek, housing Barlaam of Calabria and encouraging his tentative translations of works by Homer, Euripides and Aristotle.
In October 1350 he was delegated to greet Francesco Petrarca as he entered Florence and also have the great man as a guest at his home during his stay. The meeting between the two was extremely fruitful and they were friends from then on, Boccaccio calling Petrarch his teacher and magister. They met again in Padua in 1351, Boccaccio on an official mission to invite Petrarch to take a chair at the university in Florence. Although unsuccessful the discussions between the two were instrumental in Boccaccio writing Genealogia deorum gentilium - the first edition was completed in 1360 and this would remain one of the key reference works on classical mythology for over 400 years. The discussions also formalized Boccaccio's poetic ideas. Certain sources also see a conversion of Boccaccio by Petrarch, from the open humanist of the Decameron to a more ascetic style, closer to the dominant 14th century ethos, for example he followed Petrarch (and Dante) in the unsuccessful championing of an archaic and deeply allusive form of Latin poetry. In 1359 following a meeting with Pope Innocent VI and further meetings with Petrarch it is probable that Boccaccio took some kind of religious mantle. There is a persistent, but unsupported, tale that he repudiated his earlier works, including the Decameron, in 1862 as profane.
Following the failed coup of 1361 a number of Boccaccio's close friends and other acquaintances were executed or exiled in the subsequent purge. Although not directly linked to the conspiracy it was in this year that Boccaccio left Florence to reside in Certaldo and also was more distant from government affairs. He did not undertake further missions for Florence until 1365 and travelled to Naples and then on to Padua and Venice, where he met up with Petrarch in grand style, before returning to Certaldo. He met Petrarch only once more, in Padua in 1368. On hearing of the death of Petrarch (July 19, 1374) Boccaccio wrote a commemorative poem, including it in his collection of lyric poems, the Rime.
As mentioned he returned to work for the Florentine government in 1365, undertaking a mission to Pope Urban V. When the papacy returned to Rome in 1367 Boccaccio was again sent to Urban, offering congratulations. He also undertook diplomatic missions to Venice and Naples
Of his later works the moralistic biographies gathered as De casibus virorum illustrium (1355-74) and De mulieribus claris (1361-75) were most significant. Other works include a dictionary of geographical allusions in classical literature, De montibus, silvis, fontibus, lacubus, fluminibus, stagnis seu paludibus et de nominibus maris liber (a title desperate for the coining of the word "geography"). He gave a series of lectures on Dante at the Santo Stefano church in 1373 and these resulted in his final major work, the detailed Eposizioni sopra la Comedia di Dante.
His final years were troubled by illnesses, many relating to his great obesity.