In 1463 he became Admiral of Flanders. In 1476 he was a member of the Duchal Council of Charles the Bold. From 1477 on he was chamberlain at the court of Charles' daughter, Mary of Burgundy. In 1478 he was made a Knight of the Order of the Golden Fleece. When Wolfert VI of Borselen could no longer control the situation in the Holland and Zeeland, Joost was appointed stadtholder of these regions. He remained stadtholder until his death in 1483. Joost de Lalaing died at the siege of Utrecht, during the Hook and Cod wars.