Q. Do Catholics believe in the “great tribulation” that my Protestant friend talks about?
A. The Catholic Church affirms that “before Christ’s second coming the Church must pass through a final trial that will shake the faith of many believers [cf. Luke 18:8; Matthew 24:12]. … The Church will enter the glory of the kingdom only through this final Passover, when she will follow her Lord in His death and resurrection” (Catechism of the Catholic Church, 675, 677). This period is popularly known among both Catholics and Protestants as “the great tribulation,” based on Jesus’ description of it in the Gospel (see Matthew 24:21 and the surrounding passage; also Mark chapter 13 and Luke chapter 21).
The Catechism speaks as well about the role of the Antichrist in that tribulation:
“The persecution that accompanies [the Church’s] pilgrimage on earth [cf. Luke 21:12; John 15:19–20] will unveil the ‘mystery of iniquity’ in the form of a religious deception offering men an apparent solution to their problems at the price of apostasy from the truth. The supreme religious deception is that of the Antichrist, a pseudo-messianism by which man glorifies himself in place of God and of His messiah come in the flesh [Cf. 2 Thessalonians 5:2–3; 2 John 7; 1 John 2:18, 22].”