The Diocese of Trebinje-Mrkan is a particular church of the Catholic Church in Bosnia and Herzegovina. Established in the 10th century, is the oldest Catholic diocese in Bosnia and Herzegovina. By the number of faithful, it is also the smallest. Its seat is in Trebinje.

Lazar Lazarević was a Herzegovinian Croat Catholic priest who served as the bishop's deputy (provicar) for the Diocese of Trebinje-Mrkan from 1867, and as spiritual administrator of the Diocese of Mostar-Duvno and Trebinje-Mrkan from 1910 until 1912. Lazarević was a supporter of the independence of the Diocese of Trebinje-Mrkan from the administration of the neighboring dioceses.