Is it permissible for a Jew to become a judge in a secular judicial system if they don’t follow the Torah or even if they do?
This is a difficult question to answer.
On the one hand this appears to involve a problem. It is forbidden to take a case to a secular court of law, which will judge the case based on secular law. The Shulchan Aruch does not address the question of being a judge, which was presumably not relevant in his times, but if it is forbidden to take a case to a secular court, it stands to reason that it is likewise forbidden to judge a case based on secular law, and doing so appears to involve two problems.
One problem is that one gives legitimacy to the secular law, which is distinct from Torah Law, as if to state that their law is superior to ours. The second problem is that for civil cases this can involve gezel, “theft” from one party to the other.
However, outside Israel, where the vast majority of people who use the courts are not Jewish, the secular court is of course a perfectly legitimate institution, and involves a mitzvah (for non-Jews). It appears that there is no problem here to be part of the court, for as noted it involves a mitzvah for non-Jews, and for a Jew to be part of a non-Jewish mitzvah is also fine. There is no declaration that non-Jewish laws are superior, because in a non-Jewish court there is of course no expectation that the rulings will be based on Jewish law. There is also no issue of gezel, because litigants are non-Jews.
A problem can arise when both litigants are Jewish, and one has to rule in favor of one based on non-Jewish law. Because this case is the exception and not the rule, it appears that this will not prohibit the job. There is no “lifnei iver,” because another judge will issue the same ruling based on secular law, and the problem of mesaye’a can also be overcome (see our article on the topic for more details).
In Israel, the problem seems more severe, because a Jewish court (in a Jewish state, for a majority of Jewish people) should be issuing rulings based on Torah law, and to be part of a system that declares the superiority of an alternative legal system will appear prohibited. The gezel issue also comes to the fore in Israel, where litigants are Jewish (though as noted, this might be resolvable on a formal level).
However, there might be broader issues in Israel (such as making the system more orientated towards Torah law, and issuing rulings that come closer to Torah law), and these considerations (among others) might have been applied concerning a number of observant Jews who were judges in Israel (Justice Kister is said to have received permission from the Chazon Ish to serve on the Israeli secular court; I do not know if this is true).
It is worth adding that there is a fundamental distinction between civil and criminal law. In criminal law Torah law will agree that there is a need for making criminal laws in order to ensure the safety of citizens, and administering this law will also be permitted. Although the law of evidence is different, this will not constitute a problem, because for purposes of takanas ha-medinah we can follow alternative laws of evidence, as the Ran (Derush 11) and the Rashba (Vol. 3 no. 393) explain. In civil law, however, the matter is more problematic.
A person considering entering the profession, certainly in Israel, should therefore first consult with his rabbi.