Laura was born in Fano to Cardinal Mazarin's eldest sister, also named Laura, and her husband Count Girolamo Martinozzi da Fano, a Roman noble of an ancient family.
She was one of the Mazarinettes: the seven nieces of the Cardinal, that he brought to France in order to arrange for them rich and politically advantageous marriages.
For two years Laura lived in France under the guardianship of her uncle and "quasi stepmother", Anne of Austria.
On her sixteenth birthday, 27 May 1655, she was married to the Duke of Modena, Alfonso IV d'Este. The wedding by proxy occurred at the Palace of Compiègne with the Count of Soissons acting as the Duke of Modena. They had three children, two of which survived infancy.
Upon the death of her spouse in 1662, she became regent of Modena during the minority of her son, Francesco d'Este, Duke of Modena. She discontinued her regency in 1674.