Leonora was born in Florence, where she was brought up by Cosimo I de' Medici, Grand Duke of Tuscany and his wife Eleanor of Toledo, her aunt and namesake.

[2] In the view of art historian Gabrielle Langdon, "Her story is valuable in revealing attitudes and legalities attendant on the lives and decorum of women in the early-modern Italian court".

[3] Born at the Florentine court in March 1553, Leonora was the daughter of García Álvarez de Toledo y Osorio, Marquis of Villafranca del Bierzo and Duke of Fernandina, and Vittoria d'Ascanio Colonna.

Duke Cosimo had married his beloved daughter Isabella into the House of Orsini for political reasons, to strengthen his position on the borders of southern Tuscany.

Although Isabella had two children by Paolo Giordano, she had chosen not to live at her husband's castle at Bracciano or in Rome, where he conducted his political and amorous affairs.

Instead, with Cosimo's permission, she had remained in Florence, cultivating an artistic salon at her Villa Baroncelli in the south of the city,[h] and discreetly taking lovers, notably Troilo Orsini, a cousin of her husband's.

Though he maintained a mistress of his own,[j] much to the distress of his wife, Joanna of Austria, Cosimo's eldest son was a much less sociable and tolerant ruler than his father.

[16] Rather than attend court and participate in the artistic life of Florence, he preferred to pursue science, often locking himself up in his laboratory in the Casino of San Marco to carry out experiments in alchemy, poisons, and porcelain-making.

While he continued to cultivate the advantageous relations between her husband's house and Florence, he was less willing to turn a blind eye to the behaviour of Isabella and Leonora and to the complaints of their spouses, for whom their adultery was a question of honour rather than jealousy.

"[20] The next day, Francesco wrote to his brother Ferdinando in Rome: "Last night, around five o'clock, a really terrible accident happened to Donna Leonora.

Lady Leonora was strangled on Tuesday night; having danced until two o'clock, and having gone to bed, she was surprised by Lord Pietro [with] a dog leash at her throat, and after much struggle to save herself, finally expired.

As soon as she died, she was placed in a coffin prepared there for this event, and taken to Florence in a litter at six o'clock in the morning, led by those from the villa, and accompanied with eight white tapers [carried] by six brothers and four priests; she was interred as if she were a commoner.

Love letters and poems written by Antinori, extolling Leonora's beauty and charms in minute Petrarchian detail, were "found hidden in her foot stool".

[29] There was also a political dimension to the murders, because Antinori and another associate of Leonora's, Pierino Ridolfi—according at least to Ridolfi's confession under torture—were implicated in an anti-Medici vendetta led by Orazio Pucci.

[31] Francesco's approval meant that Pietro was never brought to justice for Leonora's murder, despite the protests of her brother Pedro Álvarez de Toledo y Colonna that her death was unacceptable.

[32] However, just over a year after the murder, Francesco exiled Pietro to the Spanish court, where he largely spent the rest of his life, visiting Florence only to beg money to pay his gambling debts.