Was Mary a virgin her whole life? What about the brothers of Jesus?

Yes. Mary’s perpetual virginity is a settled doctrine of the Catholic faith: she remained a virgin before, during, and after the birth of Jesus.

What the Church teaches. Jesus was conceived without a human father by the power of the Holy Spirit (Lk 1:34-35). The Church also confesses that Christ’s birth did not diminish Mary’s virginal integrity and that she remained ever virgin (CCC 499, 510). This teaching was held by the early Church and solemnly affirmed, including at the Lateran Council of 649. It is not merely a devotional opinion.

Who the “brothers” were. The Gospels name James, Joseph, Simon, and Judas as Jesus’ brothers and also mention sisters (Mt 13:55-56; Mk 6:3). In biblical usage, however, words translated as "brother" can describe close relatives or members of a wider kinship group. Scripture identifies James and Joseph elsewhere as sons of another Mary (Mt 27:56). The Catechism therefore explains that these passages do not refer to other children of the Virgin Mary (CCC 500).

Other biblical evidence. At the Cross, Jesus entrusted Mary to the beloved disciple John: "Behold, your mother" (Jn 19:26-27). If Mary had other biological sons, such an arrangement would have been highly unusual. The passage fits the Church’s constant understanding that Jesus was her only Son. It also reveals Mary’s spiritual motherhood toward Christ’s disciples.

What about “until” and “firstborn”? Matthew says Joseph did not know Mary "until she bore a son" (Mt 1:25). In Scripture, "until" does not necessarily imply that the situation changed afterward. For example, Michal had no child "to the day of her death," which plainly does not suggest children after death (2 Sam 6:23). Calling Jesus Mary’s "firstborn" also does not require later children. Under Jewish law, the first child who opened the womb was called firstborn because of his legal and religious status (Lk 2:22-23; Ex 13:2).

Mary’s perpetual virginity points to her complete dedication to God and to the unique identity of Jesus. When this teaching is difficult, begin with the Church’s central concern: the child Mary bore is the eternal Son, conceived by the Holy Spirit and given wholly for the salvation of the world.