The diocese is centred in the city of Banja Luka, Republika Srpska, Bosnia and Herzegovina.

Christianity arrived on the territory of the present-day diocese of Banja Luka during Roman rule in the first century AD.

After the barbaric invasion and after the settlement of Slavic tribes, these regions belonged to the surrounding dioceses: Split, Nin, Knin, Krbava and Bosnia, and the area of today's Banja Luka and the entire northern region was part of the Diocese of Zagreb.

On the Livno area was recorded the presence of Glagolitic Catholic secular priests who celebrated the Slavic liturgy.

The Catholic church in Banja Luka was particularly hard hit during the War of the Holy League (1683–1699).

In 1737 parish church in Banja Luka was burned and numerous believers migrated to the Habsburg possessions.

The Holy See started the process of beatification of 4 of them on 21 December 2014: Juraj Gospodnetić, Waldemar Maximilian Nestor, Antun Dujlović and Krešimir Barišić.

The city of Banja Luka, and much of the territory that the diocese covers contains an Orthodox Christian majority.

This is a list of Parish churches by deanery: The Diocese of Banja Luka is home to a small number of religious orders and congregations.