A trier of fact is the person or group of persons in a trial who make findings of fact as opposed to rulings of law.

In a jury trial, the jury is the trier of fact. The jury finds the facts and applies them to the law it is instructed by the judge to use in order to reach its verdict. Thus, in a jury trial, the findings of fact are made by the jury while the judge makes legal rulings as to what evidence will be heard by the jury and what the law will be that governs the case. The jury is supposed to strictly follow the law as given by the judge, but it does not always do so. In some cases this amounts to jury nullification, i.e. the jury effectively re-writing the law or blatently ignoring it in a particular case.

In a "bench trial," or non-jury trial, a judge is the trier of fact. In a bench trial, the judge makes both findings of fact and rulings of law.

In Anglo-american based legal systems, there is a strong reluctance to change findings of fact made by a jury. This principle is enshrined in the Seventh Amendment to the United States Constitution, which provides that "...no fact tried by a jury, shall be otherwise re-examined in any Court of the United States, than according to the rules of the common law."