The 'Nativity Story' is a detailed dramatization of the struggle that Mary and Joseph endured in their journey and leading up to Christ's birth. This film shows those events and dramatizes the relationship between the characters of Mary and Joseph and the bond they forge on their trek. The story begins with the decision by Mary's parents to promise her hand in marriage to a young carpenter named Joseph, who is attracted to Mary. Although she is still young enough to play with the other children, Mary's family is very poor and having seen their neighbor's daughter forced into slavery due to her family's inability to pay the King's taxes, they feel that it will be safer for Mary if she is married. As part of the agreement and due to her youth, Mary's father makes Joseph promise not to consummate their marriage for 1 year. Despite the knowledge her family is doing this for her sake Mary is unhappy because she doesn't really know Joseph and feels no love for him.
Mary is visited by an angel who tells her she will give birth to the Savior of her people as well as being told her cousin Elizabeth, who is thought too old to bare a child, is pregnant. Mary visits her cousin and shares her news as well as her fears since, by law, she was to remain pure. After the birth of Elizabeth's child Mary returns home, noticeably pregnant, and is ostracized by her entire town including Joseph because no one believes her. However, the same angel appears to Joseph and validates Mary's story which prompts Joseph to take her back which, in turn, causes the town to shun him as well.
The two must make a journey to Bethlehem, Joseph's city of origin, in order to fulfill a census order from King Herod. During their journey the two develope respect, love and trust for each other as Mary realizes how good a man Joseph is.