She was the only surviving child of Sir Francis Walsingham, Secretary of State for Queen Elizabeth I, and Ursula St. Barbe.

Sidney was appointed Governor of Flushing and left to attend his duties in the Netherlands, but pregnant with her first child, Frances waited until she had given birth.

[1] In 1590 Frances' father died, leaving her with an annuity of £300; she married again, to Robert Devereux, 2nd Earl of Essex, to whom her previous husband had left his "best sword."

The match may have been arranged by her father and took place before he died, however it caused great displeasure to the Queen, (although she forgave them relatively quickly) partly because the couple had not asked for permission beforehand.

In 1609 they built a mansion at Somerhill in Kent, and around 1618 the construction of Portumna Castle in County Galway, Ireland began.