Yes, the Virgin Mary was a virgin.
- The Madonna in Sorrow, by Sassoferrato, 17th century
Some claim that the Virgin Mary was not a virgin because of the fact that a single Latin manuscript from the fifth century left out Mary’s question (“How can this be, since I am a virgin?”) in Luke 1:34 (you can read about that claim and a response to it here), because the Bible supposedly does not say enough about the miraculous event, and because they think there was a possible translation error.
On the validity of that single Latin manuscript…
The logic behind the first reason is terrible, but even if you concede that maybe every other version of the same text is wrong (LOL), Church history shows that the Virgin Mary has always been regarded as a virgin.
The First Council of Constantinople (381 A.D.) amended the Nicene Creed to include, among other things, “…by the Holy Ghost of the Virgin Mary…”. The vast majority of Christian denominations entirely approve of that updated Nicene Creed.
The Apostles’ Creed (which is more popular in the Western part of the world than it is in the Eastern part) also mentions the “Virgin Mary”.
Even the Chalcedonian Creed (adopted at the Council of Chalcedon in 451 A.D.) mentions the “Virgin Mary”.
St. Ignatius of Antioch (who was born around the year 50 A.D. and died sometime between 98 and 117 A.D.) wrote about “the virginity of Mary” in his Epistle to the Ephesians.
St. Augustine (354 – 430 A.D.) also wrote about the virginity of Mary in his work, “Of Holy Virginity”.
On the idea that the Bible does not say enough about it…
It is written about in Isaiah 7:14, Matthew 1:23, and Luke 1:34. How much more could someone want?
On the possibility of a translation error…
The third claim also does not make sense. Here is an explanation of why from here (I encourage you to read the full explanation, as I am only featuring this single excerpt for the sake of brevity):
Whereas “almah” is translated in the KJV as “virgin” and this rendering is supported from the Greek Septuagint translation, Jewish revisers and naturalistic textual critics prefer to render “almah” as “young woman,” hoping to undercut the prophetic value of the passage. They claim that if Isaiah were really desiring to prophesy that a virgin would conceive, that he would have used the Hebrew word “bethulah”, which is claimed as a more proper word for “virgin”…“almah” is in fact a more proper term to denote virginity in Hebrew. Further, its translation by early Jewish scholars into the Greek Septuagint demonstrates that the idea of virginity was understood to be conveyed in Isaiah 7:14 and that in pre-Christian Judaism, there was no problem identifying the “almah” of Isaiah 7:14 as being virginal in her conception.
In short, yes, the Virgin Mary was indeed a virgin.