Adam Willaerts was born in Antwerp in 1577 and baptised there on 21 July. Apparently driven out of Flanders by the Counter-Reformation, his family fled across the northern Netherlands to England; in his marriage certificate Willaerts named London as his place of origin. Nothing is known about his training. In 1602, together with Salomon Vredeman de Vries, he painted the doors of an organ in Utrecht's cathedral. From then on Willaerts lived in the episcopal city, where he married Maeyken Adriaensdr. van Herwijck on 21 May 1605 and attained citizenship three years later. In 1611 he was one of the founding members of Utrecht's Guild of St Luke, and between 1620 and 1637 he held the office of dean a total of thirteen times. Willaerts's social standing was based on the political influence of the Counter-Remonstrants, who determined the city's fortunes beginning in 1618. His reputation was bolstered by his close contacts with the painter Paulus Moreelse, at that time on the city council, and with the jurists and humanist-educated art lovers Carel Martens and Arnold Buchelius. It was to these connections that the painter owed the commission to paint eight flags for the new marksmen's guild. However, Willaerts apparently enjoyed only limited prosperity, for he held no public office with the exception of the regency, assumed in November 1639, of the St Jobsgasthuis, to which he had donated a seascape eleven years before. In his old age he was dependent on public assistance, being granted a stipend of sixty gulden a year on 1 October 1654. In addition, the St Agnes convent provided him a place to live. As a caretaker there he also took charge of the Utrecht painters' association's exhibition space, which was set up in the convent in 1644. On 4 April 1664 the painter was buried in the convent chapel. Houbraken praised Willaerts as a painter of river landscapes, seascapes and harbour scenes, and particularly noted his lively, genre-like staffage scenes. His Mannerist-influenced seascapes, with which Willaerts maintained a special status in Utrecht's art scene, clearly betray his Flemish origins. Willaerts's sons Cornelis, Abraham and Isaack, as well as other pupils, were trained in the large workshop that he ran in Utrecht. That some of them only received instruction in drawing attests to Willaerts's reputation as a drawing teacher.
