Ambika along with her two sisters Amba and Ambalika was taken forcefully by Bhishma from their 'Swayamvara'( a gathering of princes where the beautiful girl chooses her own bridegroom). Bhishma challenged all the assembled Kings and Princes there and defeated them all. He presented the girls to mother Satyavati and they got married to Vichitravirya.
When Vichitravirya died at very early age, Ambika and Ambalika both were without any issue. Vichitravirya's mother sent the widows to her first son, Rishi Veda Vyasa so that the women get pregnant. When Vyasa visited Ambika, he had a dreadful appearance with burning eyes. Ambika was so frightened that she closed her eyes and did not open them for all the period of congress. When she gave birth to a son, he was born blind. The son was Dhritarashtra,who became the father of Kauravas.
When Ambika was requested by mother Satyavati to visit Vyasa again, she refused and Satyabati sent Ambalika and she gave birth to Pandu. Next time, when Ambika was requested again, she dared not to go and sent her maid instead. The maid gave birth to a son Vidura, who was raised as a Brother of Dhritarashtra and Pandu.