Said to have been the son of an Essex tailor or tanner, Gilbert, and to have been born around 1320CE, John Hawkwood served in the English army under Edward III and the Black Prince during the Hundred Years War with France, including fighting at Crecy. At some point he was knighted by the Black Prince, but history appears ignorant of the circumstances. He may initially have served under John de Vere, Earl of Oxford, since de Vere was the feudal lord of Hawkyard's birthplace, Sible Hedingham (near Braintree).
Around 1360, after the peace of Bretigny, when the official English involvement ended, Hawkwood struck out on his own and formed his own troop of men, whom he attached to the Great Company which was under the patronage of the Marquis of Monferrant/o. He is recorded at Avignon in 1361, when the pope bought off the free companies, and at the battle of Brignais in April 1362, with Bricquet and Carnelle, two other mercenary captains, when the French army were defeated by the mercenaries, but this service does not appear to have led to any great rewards.
Finally he joined (or founded) the "White Company", a band of men-at-arms, mostly English (at least to begin with). They hired themselves out as mercenaries during the 14th century Italian wars, serving (among others, and at different times) the Marquis of Montferrato, the Pisans, Pergugia, and Bernabo Visconti. In 1365 and again in 1367 his companies of men were reported destroyed, but by then his reputation allowed him to rebuuild with new recruits. His troops, though mercenaries, were never reported to have mutinied against him, in return he saw to it that they were regularly paid, by making himself attractive to employers. He did this by remaining honest to his promises, and refusing bribes to change sides: his boast was that, once he had undertaken a contract, he honoured it.
In 1372, after assisting Visconti against Montferrato, he resigned his command, allowing the Company to serve the Pope against whom they had previously fought.
In 1375 he accepted money from the city of Florence not to engage the city in battle for 3 months. The engagement lasted for over 20 years, during which time, in 1377, he married Donnina Visconti (Bernabo's illegitimate daughter) in Milan (curiously shortly after he had, on the orders of a cardinal-legate (Robert of Geneva, later to become anti-pope Clement VII), massacred the inhabitants of Cesena). His repute in this regard can be gauged by the fact that, when Geoffrey Chaucer was sent to Milan in 1378 to negotiate, on behalf of the England king, with Visconti, his instructions also required him to meet and neogtiate with Hawkwood personally.
During the 1390s, fighting for Florence against Gian Galeazzo Visconti (who had murdered Bernab), Hawkwood became the city's general and command-in-chief. He died in 1394, was given a vast public funeral and burial, and ought to have had a marble monument in the Florentine cathedral but it never came to pass. Later his body was returned to England.
A biography (1889, but still reckoned highly-readable) has been PDF'd, locatable from