All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
What this couple did before their marriage is an abominable act and it is called Zina (fornication or adultery) figuratively because it is a means that leads to Zina.
Abu Hurayrah narrated that the Prophet said: "The child of Aadam has to have his share of Zina (adultery or fornication) no matter how well he/she endeavors to avoid it. The Zina of the eyes is by gazing, the Zina of the ears is by listening, the Zina of the tongue is by talking, the Zina of the hands is by touching, the Zina of the foot is by walking [to forbidden places], and the heart desires and wishes. Then, the private parts either submit to this or deny it." [Muslim]
An-Nawawi said (while commenting on this Hadeeth) in Sharh Muslim:
"All these are types of figurative Zina." [End of quote]
It is obligatory to repent from this. However, this does not have any effect on the validity of marriage. The Zina that is meant in regard to the ruling of marrying a woman who has committed Zina, is the real Zina that necessitates the Hadd (i.e. the corporal punishment determined by the Islamic Law), which is having sexual intercourse with a non-Mahram woman.
The marriage is valid if its conditions are fulfilled, the most important of which are the (presence and consent of the) guardian and presence of two witnesses. It is not obligatory to renew the contract.
Allah knows best.