Is it lawful to marry a young man who was born outside wedlock? Actually his father and mother had sex before getting married. Eight months after his mother’s pregnancy, they got married.

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Marrying to this person is permissible if he is pious and has good qualities. His parents’ sin does not harm him.  Allah Says (interpretation of meaning): {.....No one laden with burdens can bear another's burden….}[17:15]. He also Says (interpretation of meaning): {.....Every person is a pledge for that which he has earned.}[52:21]. 

Know that an illegitimate child is not traced back to his father and does not inherit from him.  Therefore, his biological father does not become Maharam for you, thus you should not uncover yourself in front of him.

Allah knows best.