Zrinski already distinguished himself in the early twenties during the siege of Vienna in 1529, for which was awarded with a horse and golden chain. After the death of his father Nikola III in 1534, Nikola IV with older brother Ivan I inherited estates in Pounje, and they simultaneously started to fortify them as well as make contacts with the Ottomans, to whom they paid a yearly tribute like their father. However, between 1537 and 1540 they started fighting against Gazi Husrev-beg's forces for the control of fort Dubica.