Majority opinion is that it is permissible to marry the person with whom one has committed Zina, provided that the person is not a habitually unchaste person and that they both sincerely repent of their sin and that a period equal to iddah has passed since the unlawful intercourse.
إنّ من زنى بامرأة فله أن يتزوجها ولغيره أن
وهو قول ابن عمر وسالم وجابر بن زيد وعطاء وطاوس ومالك بن أنس، وهو قول
أبي حنيفة وأصحابه. وقال الشافعيّ: القول فيها كما قال سعيد بن المسيّب
One who commits fornication with a woman. It is permissible for him to
marry her and it is also permissible for another man to marry her.
And this is the saying of Ibn Umar, Salim, Jabir bin Zayed, Ata,
Tawus, Malik bin Anas. And the same is the saying of Abu Hanifa and
his companions. And from Shafi is narrated the same as that of Saeed bin Musaib [ it is permissible since a fornicator is part of the unmarried Muslim community viz 24:32 ]
وقال ابن عباس: أوله سفاح وآخره نكاح. ومَثَلُ ذلك مَثَلُ رجل سَرَق من
حائط ثمره ثم أتى صاحب البستان فاشترى منه ثمره؛ فما سَرَق حرام وما
Ibn Abbas said [about a person who married a woman he had fornicated with], his beginning was fornication and ending was marriage. His example is like that of a person who steals from a garden and then goes to the owner to buy what he stole. What he stole was haram and what he bought is halal.