The Rhinos ran out resounding 33-6 Super League Grand Final winners over defending champions St Helens to claim their second title in four years.
Smith's side had finished the regular season second to Saints but were undoubtedly the superior team when it mattered most in front of a crowd of 71,352 at Old Trafford.
The West Yorkshire club led 8-6 at the break after a tough first half in which Brent Webb had put them ahead before James Roby finished a superb break for Saints.
Leeds ran in two tries in as many minutes following the restart through Ali Lauitiiti and Scott Donald, before further scores from Lee Smith and Jamie Jones-Buchanan secured an emphatic margin of victory.
Australian Smith had previously guided Leeds to their first championship in 32 years by beating Bradford Bulls in 2004, before suffering defeat at the hands of the same opposition in the following year's final.
After their 2007 triumph, the dominant Rhinos went on to win the competition a further six times in the next 10 years.