Mielich was trained in the workshop of his father, Wolfgang Mielich, in Munich, where the important portraitist Barthel Beham also worked. From 1536 to 1539 he probably worked in Regensburg under Albrecht Altdorfer, who was to greatly influence his style. In 1541, at the behest of Duke Wilhelm IV, he travelled from Bavaria to Rome. In 1543 he is listed as a master in Munich. A second journey to Italy followed from 1552 to 1554, when he visited Titian. From 1560 to 1572 he worked on the 'Ingolstadt Altar', a masterpiece from the South German Counter-Reformation. In addition, he painted votive and epitaph paintings as well as numerous book miniatures, for example for the penitential psalms of Orlando di Lasso (1560-1561). Mielich was one of Munich's leading painters in the realm of sacred works, portraits, and book painting. His work shows a synthesis of contemporary art movements in Italy and the art of Dürer and the Altdorfer circle.