She was the daughter of Sir William Sidney,[1] of Penshurst Place in Kent, a prominent courtier during the reign of King Henry VIII, and his wife, the former Anne Packenham.

In 1555, she married (as his second wife) Thomas Radclyffe, Viscount FitzWalter,[1] who was appointed Lord Deputy of Ireland in April 1556,[1] and who succeeded his father as 3rd Earl of Sussex in 1557.

[9] Thus, it was essential he find a new suitor to produce an heir to his patronage, so much so that he expeditiously married Frances three months after the death of his wife in January 1555.

Lady Sussex was therefore motivated to devote her estate towards her passion for education and the development a new eponymous college at the University of Cambridge.

[citation needed] A 24-year-old Lady Sidney accompanied the 30-year-old Lord Fitzwalter to Ireland, arriving “upon the quay of Dublin on Whit Sunday” in 1556.

It served the Lord Deputy Sussex well until Sir Henry Sidney later renovated Dublin Castle in order to return the seat of English Government to its traditional position in Ireland.

[12] Life was difficult for Lady Sidney in Ireland, her lack of children impacted her status in the Irish public eye.

[8] This also made daily life difficult for Lady Sidney as the wives of the viceroys of Ireland were expected to be pious examples of faith.

[8] Notwithstanding, the Earl of Sussex developed a good relationship with Sean Maguire, Lord of Fermanagh, and would go on to form a strong alliance with him.

[14] While the specifics are unclear, it is understood that Maguire presented Lady Sidney with two of his finest hawks, a symbolic gift often offered in Anglo-Irish diplomacy.

In response, Lady Sidney wrote the Queen a desperate letter detailing the external forces that broke the “love of twenty-eight years continuance” even after she followed her husband “in health and in sickness, in wealth and woe”.

[8] On his death, his will is said to have been “equitable, chilling, and legalistic”[7] and he bequeathed Frances “all his jewels, valued at £3,169; 4,000 ounces of gilt plate; and the income from manors in Essex and estates in Norfolk”.

[3] Following her husband's death, Lady Sidney became very bitter and increasingly supportive of Protestantism, adopting the motto “Dieu me garde de calomnie” (middle French for “God preserve me from calumny”).

[3] In this period, Lady Sidney continued to be persecuted as the MP Arthur Hall, notoriously disreputable, published a vexatious pamphlet about her after she rejected his advances.

[25] Lady Sidney made arrangements to pay a perpetual annuity of £20 for the appointment of a biweekly lecturer at Westminster Abbey for ever, £100 to be distributed amongst the “godly ministers” of London, and £5000 for the erection and foundation of a new college at the University of Cambridge.

[27] The porcupine appears on her 24 foot high marble and alabaster funerary monument in the chapel of St Paul, Westminster Abbey.