Giovanni Antonio Bazzi was born at Vercelli in Piedmont, a shoemaker's son nicknamed "il Sodoma". After learning the rudiments of painting in his hometown, he saw Leonardo da Vinci's art in Milan around 1497 and soon incorporated his sfumato effects.

Acquiring thus the strong colouring and other distinctive marks of the Lombard school, he was brought to Siena towards the close of the 15th century by some agents of the Spannocchi family; and, as the bulk of his professional life was passed in this Tuscan city, he counts as a member of the Sienese school, although not strictly affined to it in point of style.

Sodoma lived in Siena for about eight years, then in 1508 he was invited to Rome by the celebrated Sienese merchant Agostino Chigi, and was employed by Pope Julius II, in the Camera della Segnatura in the Vatican. He executed two great compositions and various ornaments and grotesques. The latter are still extant; but the larger works did not satisfy the pope, who engaged Raphael to substitute his frescoes.

In the Chigi Palace (now Farnesina) Bazzi painted some subjects from the life of Alexander the Great. In the scene of Alexander wedding with Roxana he also painted his lover Ephasteion...

When Leo X was made pope (1513) Bazzi presented him with a picture; Leo gave him a large sum of money in recompense and created him a knight. Bazzi afterwards returned to Siena and at a later date went in quest of work to Pisa, Volterra, and Lucca. From Lucca he returned to Siena, and by 1529 Sodoma was a kind of official painter to the Sienese Republic.

Eight years later he was working beyond its borders, but he resettled there around 1545, not long before his death. He had squandered his property and is said to have died in penury in the great hospital of Siena.

Bazzi dressed gaudily, like a mountebank; his house was a perfect Noah's ark, owing to the strange miscellany of animals which he kept there. He was a cracker of jokes and fond of music, and sang some poems composed by himself on indecorous subjects.

Vasari accounted for the name as a nickname from his personal sexual tastes -

"He was a blythe and dissolute man, and kept the others in pleasure and merriment ... he always surrounded himself with boys and beardless youths whom he loved beyond measure, so that he got the nickname Sodoma, and he was not upset, he was proud of it, composing on it poems and songs and singing them quite pleasingly with his lute."

On his 1531 tax return, Sodoma listed among his possessions a monkey, a raven, an owl, a peacock, over thirty grown children, and "three wicked brutes, that is, three women." Long before the concept of a "Bohemian" lifestyle existed, he perfected an anti-middle-class way of living.

As he advanced in age he became too lazy to make any cartoons for his frescoes, but daubed them straight off upon the wall. Bazzi produced at intervals some works of very fine quality, and during his lifetime his reputation stood high.

His most celebrated works are in Siena. In S. Domenico, in the chapel of St Catherine of Siena, are two frescoes painted in 1526, showing Catherine in ecstasy, and fainting as she is about to receive the Eucharist from an angel. In S. Francesco are the Deposition from the Cross (1513) and Christ Scourged; by many critics one or other of these paintings is regarded as Bazzi's masterpiece. In the choir of the cathedral at Pisa is the Sacrifice of Abraham, and in the Uffizi Gallery of Florence the highly homoerotic St Sebastian.