A grandniece of Elizabeth's mother, Anne Boleyn, and close to Elizabeth since childhood, Lettice Knollys was introduced early into court life. At 17 she married Walter Devereux, Viscount Hereford, who in 1572 became Earl of Essex. After her husband went to Ireland in 1573 she possibly became involved with Robert Dudley, Earl of Leicester. There was plenty of scandalous talk, not least when Essex died in Ireland of dysentery in 1576. Two years later Lettice Knollys married Robert Dudley in private. When the Queen was told of the marriage she banished the Countess forever from court, effectively curtailing her social life. The couple's child, Robert, Lord Denbigh, died at the age of three, to the great grief of his parents and ending all prospects for the continuance of the House of Dudley. Lettice Knollys' union with Leicester was nevertheless a happy one, as was her third marriage to the much younger Sir Christopher Blount, whom she unexpectedly married in 1589 only six months after the Earl's death. She continued to style herself Lady Leicester.
The Countess was left rich under Leicester's will; yet the discharge of his overwhelming debts diminished her wealth. In 1604–1605 she successfully defended her widow's rights in court when her possessions and her good name were threatened by the Earl's illegitimate son, Robert Dudley, who claimed that he was his father's legitimate heir, thus implicitly declaring her marriage bigamous. Lettice Knollys was always close to her large family circle. Helpless at the political eclipse of her eldest son, the second Earl of Essex, she lost both him and her third husband to the executioner in 1601. From the 1590s she lived chiefly in the Staffordshire countryside, where, in reasonably good health until the end, she died at age 91 on Christmas Day 1634.