His first dated picture, the "Regents of the Walloon Orphanage in Amsterdam", dates from 1637. The style of this painting suggests that in Amsterdam van der Helst may have trained with Nicolaes Eliaszoon Pickenoy. His first important commission was for a large "schuttersstuk" known as the "Civic Guard led by Captain Roelof Bicker and Lieutenant Jan Michielsz. Blaeuw". Van der Helst received the commission in 1639 and finished it in 1642. The large 7.5m wide canvas was hung over the fireplace of the grand assembly of the Kloveniers guild, the same room for which Rembrandt painted "The Night Watch". The success, which the artist achieved with this composition, led to many commissions for single and double portraits of Amsterdam's leading class such as his "Portrait of Andries Bicker", the mayor of Amsterdam. The city's military brass and wealthy members of the regent class all had portraits made by van der Helst.