How does the Catholic Church choose Saints?

Answer 1

The Church doesn't choose saints. God does that. The Church recognizes and publicly proclaims them so the faithful may benefit from their example. Very generally, the church seeks to verify two miracles in the name of the person before declaring sainthood.

First, you have to die. Once you have been dead at least 5 years a cause
for sainthood can be opened. The local bishop or other religious leader
will assign someone to collect all sorts of documents and conduct
interviews about the life of the candidate. Once they have all the
information, the file will be sent to the Sacred Congregation for the
causes of Saints in Rome. They will study the file and, if it seems the
person exhibited some form of heroic virtue, that person will be declared
a Servant of God and an official Cause for Sainthood will be opened.

More investigations and interviews will be conducted and if the person
passes all favorably, they will be named as Venerable.

Next, more investigations and at least one miracle must be confirmed and
verified due to the intercession of the candidate. If all goes well, the
candidate will then be Beatified by the Pope and receive the title of
Blessed. Mother Teresa of Calcutta is at this stage right now.

In the final stage, more investigations and at least one more miracle must
be verified. Once all that has been done, the file is turned over to the
pope who will make the final decision. It will be up to the pope to
declare a person a saint and then arrangements are made for the official
canonization ceremonies.

This process can take many years, even centuries.

Of course, the person became a saint the moment they entered heaven. The
Church just needs to investigate to make sure the candidate is worthy of
emulation and makes a good role model for future generations.

Answer 2

The Catholic Church follows a rigorous process known as canonization to declare individuals as saints. This process involves thorough investigation into the person's life, virtues, and miracles attributed to their intercession. After being declared venerable, the person needs to be recognized for posthumous miracles to be beatified and later canonized.