The Last Supper is traditionally observed on Holy Thursday , the Thursday before Good Friday. Historically, some scholars argue it may have been Wednesday evening instead, so the exact day is debated.

Quick answer

  • Church tradition: Holy Thursday.
  • Some historical theories: Wednesday evening, based on different Gospel chronologies.
  • Bottom line: If you want the standard Christian observance, the answer is Thursday.

If you want, I can also explain why some sources say Wednesday and others say Thursday.