Central Election Committee head and High Court Justice Yitzhak Amit ruled that Yamina MK Silman was permitted to run with the Likud.
Silman entered the previous Knesset as a member of Yamina, and then announced in April that she was leaving the coalition, ending its 61-member majority.
Amichai Chikli's candidacy was barred after MK Gaby Lasky petitioned the Central Election Committee, claiming that he did not resign early enough to be allowed to run on a different list.
Meretz accused Silman of leaving the coalition after receiving offers from the Likud for the next election, which is illegal according to the election laws.
The exchange began with a comment Shaked made to Yediot Ahronot and Ynet on Sunday in light of her breaking off from Yoaz Hendel and the Zionist Spirit party.
Questions involving a number of Israeli political parties will need to be decided until Thursday's deadline, and could lead to last-minute drama.
More than twice as many coalition voters in 2021 say they will change blocs than opposition backers.
Ayelet Shaked is the leader of the Zionist Spirit party that she formed with Communications Minister Yoaz Hendel.
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If Silman wishes to run in a different party in the upcoming election, she will now have to resign from the Knesset.