Pumpkin was bred by Mr John Pratt, who also owned his dam, the remarkable Old Squirt Mare. Squirt Mare (ch f 1750 Squirt), bred by the Duke of Bolton, produced seventeen foals between 1755 and 1774. Two of them died young, three were never trained and the other twelve were good runners. Amost all of Family 24 descends from her, including the influential stallion The Baron (ch c 1842 Birdcatcher). She died in August of 1777.

Prior to his turf career Pumpkin was purchased by the Hon Thomas Edward Foley, later 2nd Baron Foley, who also owned Firetail (b c 1769 Squirrel). He was sold before the start of his final year on the turf, 1776, to Mr Codrington, and then half way through this year he was again sold to the Rt Hon Charles James Fox, a racing confederate of Lord Foley.

From twenty-four starts he won sixteen races worth 6,090 guineas, nine hogsheads of claret and the Newmarket October Cup, valued at over one hundred guineas. His victory in his very first race in 1772 by half-a-neck over the favoured Denmark was thought to be one of the finest ever run.

In spite of his distinction on the racecourse and his impeccable pedigree Pumpkin was at best mediocre in the stud, as reflected in his declining fee. He stood at Rushbrook, near Bury, Suffolk, in 1777 and 1778, for a fee of ten guineas, the following two years at the Green Farm, near Stoney Stratford, Buckinghamshire, for five guineas, and in 1792, at Highflyer Hall, near Ely, Cambridgeshire, for two guineas.

His best offspring was his daughter Seedling (b f 1784), bred by Lord Foley, the dam of the Ascot Gold Cup winner Master Jackey (ch c 1804 Johnny) and the Woodcote Stakes winner Miss Seedling (b f 1806 Totteridge). Another daughter, Pumpkin Mare (b f 1785), produced Lady Bull (b f 1796 John Bull), also called Lady Jack Bull, who was sent to Virginia in 1799 where she was trained but had no success on the turf.