István Kendi married twice: his first wife was Zsuzsanna Csapy, stepdaughter of Prince Sigismund Rákóczi, the second one was Anna Horváth de Palocsa since 1618.
He participated in the uprising of Mózes Székely in 1603 and was captured by General Giorgio Basta for a short time.
After the resignation of János Petki, he was appointed Chancellor of Transylvania by Prince Gabriel Báthory from whom he received the castle of Szamosújvár (today: Gherla, Romania) as a donation in 1609.
On 20 March 1610, Boldizsár Kornis, the Captain General of the Székelys, and he tried to kill his guest, Báthory with an assassin in his estate, Szék (today: Sic, Romania), however the hired man exposed them.
Kendi received amnesty from the new Transylvanian ruler Gabriel Bethlen and became again a member of the Royal Council in March 1614.