Pieter Casteels was born in Antwerp, on 3 October 1684, the son of the painter Pieter Casteels. He was trained by his father and in 1708 arrived in London with his brother-in-law, Peter Tillemans, having been offered work by a picture dealer. He settled readily into London's artistic community, subscribing to Kneller's Great Queen Street academy in 1711 and becoming a member of the Rose and Crown Club. Although he returned briefly to Antwerp in 1716, Casteels settled permanently in England where he was a leading painter of flowers and exotic birds, chiefly for overdoors and chimney-pieces. His range as a decorative painter also encompassed small history pictures in architectural settings. However painting provided only a part of his income: he also imported fine pictures from the continent and his patrons included James Stanley, 10th Earl of Derby. Between September 1722 and May 1724 Derby spent just under £2,500 on seventeen Italian and Flemish paintings supplied by Casteels and £10 on a flower piece by Casteels himself.
In 1726 Casteels successfully launched a subscription for a set of twelve prints of birds which he had etched after his own designs, this being his first work of that kind. This project encouraged him to undertake the publishing venture Twelve Months of Flowers and the Twelve Months of Fruit (The Twelve Months of Flowers, a floral calendar of still lifes, 12 paintings, sold Christie's, New York, 25 May 2005, lot. 11, $1,640,000).
By advertising the usefulness of these sets of prints as patterns for workers in luxury industries, Casteels drew attention to his own potential as a textile designer. In May 1735 he retired from painting and spent his last fourteen years working for a calico manufacturer as a residential artist, first at Martin Abbey near Tooting, Surrey, and later, briefly, in Richmond, Surrey. He died in Richmond on 16 May 1749 after a lingering illness, and was buried there. A sale of his collections, including copper plates, was announced by the auctioneer Richard Ford in the General Advertiser on 6 March 1750 and the plates of his Birds were acquired by the printseller John Bowles.