Isack van Ostade was baptised in Haarlem on 2 June 1621 as the youngest son of Jan Hendrick van Eyndhoven, possibly a linen weaver, and Janneke Hendriksen. His brother Adriaen van Ostade (1610-1685) gave him his training. Beginning in 1639 he has dated works from each year. In 1641 the Rotterdam art dealer Leendert Hendricx ordered pictures from him, the delivery of which led to a quarrel that was ended only in 1643 with a compromise before the Haarlem Guild of St Luke. Isack joined the guild in that year. He died young, and was buried in Haarlem the week of 16 October 1649.
At the beginning of his brief career Isack painted pictures of peasant interiors like those of his brother Adriaen. Then, around 1542, he began painting farmers in front of landscape or village backgrounds. Among his most common motifs are travellers in front of a tavern, farmers at work on a wide variety of chores, slaughtered pigs, depictions of children and winter landscapes. Occasionally he also supplied staffage figures in works by other painters, among them Jacob van Mosschers. Some of his works employ remarkably large formats. He was also a productive draughtsman. In addition to the model of his brother, with whom he remained close, he was influenced by Pieter van Laer and Jan van Goyen. Claes Molenaer, Cornelis Decker, Roelof van Vries, Jan Wijnants and Johannes Oudenrogge are closely related in style. Gerrit van Hees produced copies of his works.