And that avenged last year's final defeat at the hands of the Scarlets. The Scarlets took the lead after nine minutes courtesy of a try from scrum-half Justin James, but a Lee Halfpenny penalty reduced the arrears midway through the half.
Daniel Evans, who has been one of the competition's best players this season, improved the lead with a penalty before the Ospreys went ahead thanks to a try from prop Ryan Bevington. Halfpenny's conversion provided a 10-8 interval lead.
In the second half there was more of the same from the Ospreys as the Scarlets failed to register a single point and subsequently relinquish the title they won at the Millennium Stadium last season. Halfpenny bagged a penalty to increase the lead to 13-8 and Luke Hathaway made it safe with a try that Halfpenny improved in the final quarter.
Coach Phil John said, "We are absolutely delighted for the boys. They have worked hard all season to reach this final and they worked hard on the night to win it. It was a determined, tenacious and tactically aware performance. We struggled a little in the first half, but we asserted ourselves in the second half. I thought our defence was very good in the second half."
Ospreys: Tries - Bevington, Hathaway; cons: Halfpenny (2); pens: Halfpenny (2)
Scarlets: Try - James; penalty - Evans