It is ḥarām and it does not achieve anything. After an irrevocable third divorce Allah says she is not lawful for him "until she marries a husband other than him" — and the majority of scholars hold this means a genuine marriage entered with the intention of permanence, followed by consummation, and then ended naturally by death or divorce; the Prophet ﷺ told the wife of Rifāʿah, "Do you wish to return to Rifāʿah? Not until you have tasted his sweetness and he has tasted yours" (agreed upon). A pre-arranged marriage whose purpose is to legalise her return is a sham contract: it is authentically reported that the Prophet ﷺ cursed the muḥallil (the one who makes her lawful) and the muḥallal lahu (the one for whom she is made lawful), narrated by Aḥmad, al-Nasāʾī and al-Tirmidhī. The Mālikīs, Ḥanbalīs and the verifying scholars hold such a contract void outright, and even those who would treat it as technically binding regard it as gravely sinful. The correct response to a triple divorce is patience and acceptance of Allah's decree, not a contrived contract.
Q&A · Marriage & Divorce
What is the ruling on a halāla marriage to make a woman lawful for her first husband again?
Evidence — the daleel
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.