Can a Ger serve on a Bais Din?
Shalom, There are many different opinions regarding your question, all of them cited by R. Eliezer Waldenberg (Tzitz Eliezer vol. 19, ch. 47). Many (like the Aruch HaShulchan) say that it’s okay if his father was Jewish, which, incidentally is very often the case among (most?) converts today (Shulchan Aruch, Choshen Mishpat 7, 1). The Rashbatz brings that Shmaya and Avtalyon, the heads of the Sanhedrin were converts to Judaism, and accordingly, it would be allowed. On the other hand, the Rambam says that it is prohibited. If so, some explain that if they are the greatest scholars available at the time in a certain place, than it is allowed. Many (e.g. the Knesset HaGedola, Aruch HaShulchan, etc.) say that if the parties involved accept him as a dayan (which is usually the case), than there’s no problem, but the Nodah B’Yehuda, disagrees. If you are asking for a particular ger who wants very much to be a dayan, you can tell him that if he invests sufficient time and effort into his learning, there are more than enough places and situations where he can serve as a dayan on a Beit Din! With Love of Israel! Rav Ari Shvat