The Seahawks were leading 15-0 late in the second quarter when Smith picked off Denver's Peyton Manning and rambled 69 yards for a score.
Percy Harvin opened the second half with an 87-yard kickoff return for a touchdown and the rout was on for the Seahawks, who became the first team in Super Bowl history to score on a safety, an interception and a kickoff return.
On defense, Seattle forced four turnovers that led to 21 points and limited the Broncos -- who boasted the best offense in NFL history -- to just 27 rushing yards en route to the first Super Bowl victory in franchise history.
Russell Wilson completed 18-of-25 passes for 206 yards with TD passes to Jermaine Kearse and Doug Baldwin.
Kearse and Baldwin combined for nine catches for 131 yards and Marshawn Lynch led the Seahawks' rushing corps with 39 yards and a score on 15 carries.
Manning threw for 280 yards on 34-of-49 efficiency with two interceptions and a touchdown, falling to 1-2 in his three career Super Bowl appearances.
Demaryius Thomas made a Super Bowl-record 13 grabs for 118 yards with a score.