At the age of twenty he was secretary to King Władysław Jagiełło, and fought with him in the battle of Grunwald on 14 July 1410. A favourite with the king, he took part in the management of the country's most important affairs. His influence with the king greatly aided him in opposing the Hussites, who had gained royal favour. On 9 July 1423, he was appointed to the episcopal See of Kraków, and in 1433 he was sent by the king as legate to the council of Basle, where he endeavoured to be on friendly terms with both parties.