Leopold was the founder of the branch of the dynasty from which all the Habsburgs of the Early Modern era were to trace their descent.
In 1365 at the age of fourteen his brother Rudolf arranged for him to be married to Viridis Visconti, who was about his own age. The Visconti ruled over the extremely wealthy region of Lombardy, and the bride’s father Bernabò was involved in numerous conflicts with the pope and thus on the lookout for allies in the Holy Roman Empire. Thanks to his numerous children, whom he systematically married to princes of the Empire, he had a network of relatives among the leading families of the Empire. These unions played a not unimportant role in spreading the ideas of early Humanism north of the Alps.
By marrying into this powerful northern Italian dynasty, the Habsburgs found an ally in their efforts to secure their rule in Tyrol.
The marriage between Leopold and Viridis resulted in numerous children.
The fact that the first four children were sons, namely William (1370–1406), Leopold IV (1371–1411), Ernest (1377–1424) and Frederick IV (1383–1439), who survived into adulthood, inevitably brought about the further fragmentation of the dynasty into various branches. This would become the cause of intrafamilial conflicts, as soon became evident.
The names of three of their daughters are known: together with Elizabeth (1378–1392) and Catherine (after 1380), of whose lives we know almost nothing, mention should be made of Margaret (c. 1370–after 1400), who was married to John Margrave of Moravia, a son of Emperor Charles IV from the House of Luxembourg.