I saw a similar question, hope I'm not being redundant.
I wanted to know if marriages on Shabbat are allowed, and if not, where is it said, and why not. Thanks in advance! It is a pleasure!
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Shulchan Aruch OC 339:4 rules that one should not perform Kiddushin (betrothal) or Nissuin (marriage) on Shabbat or Yom Tov. However he notes that if one did so, even on purpose, it works and the couple is fully married.
The prohibition originates in the Mishna (Beitza 5:2). The Babylonian Talmud (36b per Tosfot) explains that this is a rabbinic prohibition because marriage resembles a business transaction which is prohibited on Shabbat.