Appointment of Catholic bishops

The appointment of bishops in the Catholic Church is a complicated process. Outgoing bishops, neighbouring bishops, the faithful, the apostolic nuncio, various members of the Roman Curia, and the pope all have a role in the selection. The exact process varies based upon a number of factors, including whether the bishop is from the Latin Church or one of the Eastern Catholic Churches, the geographic location of the diocese, what office the candidate is being chosen to fill, and whether the candidate has previously been ordained to the episcopate.

Initially, bishops were chosen by the local clergy with approval from the Holy See in Rome as it is done today. The early church fathers attest to the fact that the Church of Rome - in effect its diocese - was the central point of authority. They attest to the church’s reliance on Rome for advice, for mediation of disputes, and for guidance on doctrinal issues. They note, as Ignatius of Antioch (ca 1st century) does, that Rome "holds the presidency" among the other churches, and that, as Irenaeus (ca 2nd century) explains, "because of its superior origin, all the churches must agree" with Rome. They are also clear on the fact that it is full communion with Rome and the bishop of Rome that causes one to be in communion with the Catholic Church. This displays a recognition that, as Cyprian of Carthage (3rd century) puts it, Rome is "the principal church, in which sacerdotal unity has its source." By the time of the First Council of Nicaea in 325, the metropolitan bishop had a role of the greatest importance in the selection. The Council decreed that the consent of the metropolitan bishop was normally required.

...
Wikipedia