The singer, 24, and the model, 21 - worth $250 million and $2 million respectively - exchanged vows on the same day they obtained their marriage licence at the courthouse on September 13, TMZ claims.
The couple had a preacher on hand, Jeffrey Quinn, a member of the faculty at Nyack College near the courthouse, while the Baby hitmaker's friend Josh Mehl was the witness at the ceremony.
The site reports Hailey and Justin asked lawyers for a prenup the same day, but an legal agreement is unable to be drafted and signed so quickly - meaning that they got married without a prenup in place.
Furthermore, the couple have made no movement to have an agreement drawn up now they are legally married.
A source claimed Justin is 'so in love and doesn't see the need for one'.
The couple are still said to be planning a formal ceremony, but it will be simply symbolic now they are officially husband and wife.