Smith is the first Buckeyes quarterback to win the O'Brien, which started honoring the top quarterback in 1981.
Colt Brennan of Hawaii was the other finalist.
Smith, Quinn and Arkansas running back Darren McFadden are the finalists for the Heisman Trophy, which will be handed out Saturday night in New York. Smith is the heavy favorite to win the Heisman.
Smith is fourth in the nation in passer rating (167.9) with 2,507 yards, 30 touchdown passes and only five interceptions. He'll lead No. 1 Ohio State against No. 2 Florida for the national title on Jan. 8 in Glendale, Ariz.
Last year's O'Brien winner was Texas' Vince Young.