Bianca Maria Visconti was born on 31 March 1425 as the illegitimate daughter of Filippo Maria Visconti, Duke of Milan and Agnese del Maino. Her mother served as lady-in-waiting to Filippo’s wife, Beatrice di Tenda, who was tortured and executed on her husband’s orders before Bianca’s birth. Agnese and Filippo had a second daughter, named Caterina Maria or Lucia Maria, but she died not long after her birth.
Bianca and her mother were sent to live in Abbiate when she was just six months old, and it was there that she received a humanist education. Her father visited her often.
In 1430, Bianca was betrothed to Francesco I Sforza, who was 26 years older than her but her father tried to dissolve the betrothal twice in later years. They were married in the Abbey of San Sigismondo on 24 October 1441. She was appointed as regent of the Marche in 1442, while Francesco was away on a military campaign. Their first child was born in 1444, and they would go on to have nine children, though not all would live to adulthood.
Her father’s death in 1447 led to Milan declaring the Ambrosian Republic. Bianca and Filippo marched on Milan, and it was reported that Bianca donned armour and actually fought in a battle. In 1450, Francesco was at last declared Duke of Milan, with Bianca as his Duchess. Bianca was not to be a non-political consort, and she devoted herself to duchy’s administration.