Is living in a "non-valid" marriage a mortal sin?

If marriage is not blessed by the church and it’s not considered a “valid” marriage, is the couple living in mortal sin?

Dear Anjel,

If two people are living as husband and wife and are not married, they are living in mortal sin. This is how the Church views marriages that are not valid. The objective in such a situation would be to contact a priest to rectify the matter by entering into a valid marriage.

Fr. Vincent Serpa, O.P.

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