Beautiful song!
Yes, it is, though it is not an original composition of the vocal group performing [at the youtube link previously provided].
But then you likely had heard the song before? The Pentatonix cover of it is presently enjoying a fair amount of radio airplay.
As to the song's lyrics and musical arrangement;
In 1984, Lowry wrote the lyrics to the song "Mary, Did You Know?", when asked to write a script for a church Christmas play. Lowry wrote a series of questions that he would like to ask Mary, the mother of Jesus. These questions were used in between the scenes of the play. Over the next decade, Lowry tried to find the music that would complete the song. Twelve years after writing the lyrics, musician and songwriter Buddy Greene wrote the music to the song. The Christmas play script then became the song.The song has become a popular Christmas song performed by more than thirty artists including Cee Lo Green, Clay Aiken, Kenny Rogers, Wynonna Judd, Michael English, Daniel Childs, Natalie Cole, Pippa Wilson, Kathy Mattea, Michael Crawford, and Pentatonix.