She was the only surviving child of Sir Francis Walsingham, Secretary of State for Queen Elizabeth I, and Ursula St. Barbe. A lady-in-waiting to Queen Elizabeth, she married Philip Sidney in 1583, a match arranged by her father over the objections of the Queen, possibly because she did not like the prospect of two close councillors forming a power block. 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. Her daughter was born in 1585 and named Elizabeth after the Queen, who had forgiven the couple and was one of the godparents. In June 1586 Frances left England for the Netherlands to meet her husband. On 22 September, Sidney was injured at the battle of Zutphen, and the wound became infected. Frances, again pregnant, nursed him, but he died on 17 October. She brought his body back to England, where he was given a hero's funeral, but miscarried their child.
Second marriage
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, partly because the couple had not asked for permission beforehand. Frances had three children who survived infancy with her second husband, these were named Frances, Robert and Dorothy. Her husband Robert was executed in 1601 after participating in an attempted coup against the Queen. Frances attempted to see the queen to plead on his behalf, but was not permitted to see her. Her son became the third Earl of Essex.
Third marriage
In 1603, she married her third husband Richard De Burgh, Earl of St Albans and Clanricarde. They had one son, Ulick, and two daughters; the first, Honora, and the second known as Margaret or Mary. Together they lived in both Ireland and England, building great houses in each country. In 1609 they built a mansion at Somerhill in Kent, and around 1618 the construction of Portumna Castle in County Galway, Ireland began. She died early in 1632 at Somerhill, and was buried at St Peter and St Paul, Tonbridge, where she and her husband have effigies.