Lely was born Pieter van der Faes to Dutch parents in Soest, Westphalia, on 14 September 1618, the son of Johan van der Faes and Abigail van Vliet. As Pieter Lely (Lely being the name of the street in a fasionable quarter of The Hague where his forebears had settled, the house featuring a lily carved on the gable) he is recorded in the minutes of the Guild of Saint Luke in Harlem for October-November 1637 as one of the pupils of Frans Pieters de Grebber. Unlike many of his contemporaries he never visited Italy.
When Lely came to London during the early years of the Civil War (the exact date is unknown), his bent was for pictures and historical compositions. He continued to paint such works and portraits of musicians with their instruments until the early 1650s. But from the start he accommodated himself to the native demand for portraiture, espoused by aristocratic patrons who, supporting the Parliamentary cause, had remained in London. In 1647 he became a member of the Painter-Stainers Company and by 1654 was described as "the best artist in England."
After the Restoration in 1660 Lely was recognized as Van Dyck's successor as court and society painter; he became Principal Painter to King Charles II in 1661 and was granted naturalization in 1662. With rapidly increasing demand he built up an elaborate studio organization and method by the early 1670s; a pose would be selected from an existing set of numbered postures, he would paint the head from life, chalk in the pose, and lay in the colors, leaving the rest to one of his many assistants. His output was immense.
Lely worked unremittingly and, emulating Van Dyck, led a grand and extravagant life in his house on the piazza, Covent Garden. A lover of music and close friend of poets, he also amassed a fine collection of paintings and sculpture and a huge collection of drawings, all bought largely at the sales following the dispersal of collections after the Civil War. He also purchased paintings and drawings by Van Dyck from the artist's widow. Lely's collection was the first in England to be systematically stamped with a mark. The collection was sold after his death to pay off debts, and at the time (1682) this was by far the most important public auction of pictures in England. Nothing is known of his mistress, Ursula, whom he married after the birth of two children and who died in childbirth, with her infant, in 1674. In the later 1670s his career was threatened by the increasing success of an ambitious young rival, Godfrey Kneller, who had come to England in 1674, but Lely remained in favor and was knighted in 1680. He died in London on 7 December 1680.
[Hayes, John. British Paintings of the Sixteenth through Nineteenth Centuries. The Collections of the National Gallery of Art Systematic Catalogue. Washington, D.C., 1992: 160-161.]