The agency will use oversee an integrated PR campaign to highlight the match as one of the biggest sporting events in the UK this year.
It will target a broader consumer audience beyond core rugby fans to raise the fixture's profile.
The appointment follows Four SAS' work with Premier Rugby last season during which the agency implemented a multi-channel promotional campaign to support tickets sales for the 2008 Final. Using a combination of traditional and new media tactics the campaign culminated in a world record 81,600 crowd at Twickenham Stadium.
Neil Hopkins, Four SAS Head of Sport said: ‘Last year's campaign demonstrated how effective PR can be in driving sales. Despite not knowing the finalists until two weeks before the game, the campaign had gained such momentum that a large percentage of the seats had already been sold.'
The 2009 Guinness Premiership Final takes place on Saturday, 16 May.