About 1600-16O3 he was trained in the workshop of Karel van Mander who is most remembered for his writings on the history of art. In 1610 he became a member of the Lukas Guild, and in 1644 its head. He was highly esteemed in Haarlem, as is shown by the fact that he received altogether eight commissions for the large civic guard pictures. But Hals was often in debt as his portraits were not "elegant" enough for contemporary taste, so that he never became a fashionable painter. Also, he had to provide for ten children from his two marriages. In 1652 he had to auction his furniture and his paintings to pay the baker, and shortly before his death he received poor relief in the form of money and peat. It is often maintained that his poverty was the result of his extravagant lifestyle, but there is no evidence for this.

Hals is the most important Dutch portrait painter. His surviving work comprises about 300 paintings, and the majority of these are portraits and group portraits. Although also a genre painter after 1626 when he had become familiar with the Utrecht Caravaggists, these still remained portraits except that they also contained symbolic accessories or were painted in a narrative manner. Hals certainly was the foremost painter of the Dutch group portrayal. Already with his first commission, 1616, the "Banquet of the Officers of the St George Civic Guard", he revolutionised this branch of painting which had so far been restricted to lining up several single portraits. But he never presented the scene in a theatrical fashion, as Rembrandt did with his "Night Watch", and each of his sitters is given individual and equal attention. His last two group portraits were the "Regents" and "Regentesses of the Old Men's Almshouse in Haarlem". These represent the end of the great era of this type of painting - there are just a few examples of it in the 18th century, and with its waning, the vitality and Baroque theatricality are replaced by a pessimistic, melancholic resignation about the human condition.

In his large single or double portraits, as in the lif-size "Portrait of Wilem van Heythuysen", Flemish elements and the influence of Rubens become evident, with the background showing views and scenic staffage. His special devices used for livening up the picture are most evident in his genre portraits ("The Gypsy Girl", "The Merry Drinker", "Malle Babbe"). With a spontaneous and seemingly improvised brushstroke, he produces light reflections on the faces, objects, cloth and lace, thus creating an effect of immediacy as well as vitality. Apart from his son Dirck and the imitator of his style, Judith Leyster, his pupils included the Ostade brothers; he also greatly influenced Steen and Terborch.