Before his rule, early in his life, Ninoslav was an opposer of the Bosnian Church, a faithful Hungarian supporter and a pious Catholic Christian.

Entering his rule, Matej Ninoslav forcibly replaced his predecessor, Stjepan Kulinić with the help of the adherents of the Bosnian Church, which caused good relations with Serbia to sour.

The Prenestine Bishop James, serving as the Pope's legate, finished a business in Hungary and came to Bosnia to influence Matej Ninoslav to give a statement that he will remain a Catholic, even though his ancestors were adherents of the Bosnian Church.

The Roman Pope wrote a letter to Matej Ninoslav thus on 10 October 1233, guaranteeing his integrity and putting him under his protectorate: Hugging you with true love, your person and your land of Bosnia.

To make matters worse; the Pope was unsatisfied with the Krstjani in Bosnia; so he replaced the old, presumably strayed Bosnian Bishop, in 1233, with a German member of the Dominican Order Johannes Wildeshausen.

On 9 August 1235, the Pope also confirmed King Andrew's proclamation of Croatia's Herzog Coloman as the legitimate Ban of Bosnia.

The war lasted for almost five years and was exhausting for both sides as can be seen in the fact that Bishop Wildeshausen begged the Pope to relieve him from his duty.

Although the Crusaders managed to freely overrun the Western Areas and the Hum they could never get a permanent hold of Bosnia proper.

In 1237, deemed incapable, Bishop Wildeshausen was replaced by the Pope with a Hungarian Dominican, who conducted terror by burning the Bogomils on stakes.

Ninoslav lost Split, as the Hungarian Army, under Slavonia's Ban Dionisus, together with the forces of Trogir took the city in the summer of 1244.

Bosnia was not harmed itself by the King's military campaign and a peace was signed on 20 July 1244 with Ban Ninoslav and his brothers and nobility, that confirmed the rights and lands of the Bosnian Church.

The situation grew very dangerous, so Ninoslav wrote to the new Pope that he always remained a staunch Catholic Christian, and never a heretic.

Eventually, King Bela IV conquered and pacified Bosnia and succeed in putting Ninoslav's Catholic cousin Prijezda as the Bosnian Ban.