Courtier and heiress. She was the daughter of Josceline Percy, eleventh earl of Northumberland (1644–1670) and Elizabeth, née Wriothesley, daughter of Thomas Wriothesley, fourth earl of Southampton.

Josceline died abroad shortly after Elizabeth's birth, and the entire Percy property and fortune, with the exception of the title itself, passed to the infant Elizabeth, making her the most eligible spinster in the country. Betrothals were engineered by her grandmother, widow of the tenth earl of Northumberland. In 1679 Elizabeth was married at 12 to her first husband, Henry Ogle, heir to the dukedom of Newcastle, but he died sickly the following year. Her second husband was the much older and notorious Thomas Thynne, whom she found repulsive, and she fled to the Netherlands and sought shelter from the British ambassador. While there a nobleman named Count Königsmark fell in love with Elizabeth, and ordered Thynne's assassination while his coach was driving down Pall Mall. While Elizabeth denied complicity, the murder of her second husband blotted her reputation. Finally, in 1682, she married Charles Seymour, the sixth duke of Somerset (1662–1748). While this marriage was more successful, the match was not a happy one on account of the duke's inordinate pride.

The now duchess of Somerset served as a Lady of the Bedchamber to Queen Anne from 1702, and by 1711 she was very highly thought of by her. When Sarah, duchess of Marlborough was dismissed from her officee as Groom of the Stole, Elizabeth replaced her. The duchess of Somerset was discrete and gentle, and this failure to badger the Queen bolstered her esteem with Anne.

Anne died in 1714, and Elizabeth retired until her own death, at Northumberland House on the Strand, in 1722. She was taken to Salisbury Cathedral and buried there after a grand funeral.