Peat announced his decision through the school Tuesday. The 6-foot-7, 316-pound Peat is considered one of the top tackles in the country.
Peat had some lapses early in the season, mostly in pass protection, as the Cardinal worked in four new starters on the offensive line. He finished strong and won the Morris Trophy as the Pac-12's top offensive lineman and earned second-team AP All-America honors.
Peat, whose father Todd played six seasons in the NFL, is the second Stanford player to declare early for the draft. Junior cornerback Alex Carter, whose dad Tom also played in the NFL, announced his decision to leave last week.
Quarterback Kevin Hogan is still weighing whether to return as a fifth-year senior.