The 2008–09 Guinness Premiership was the 22nd season of the top flight of the English domestic rugby union competitions, played between September 2008 and May 2009.

Northampton Saints gained promotion to the league this season by finishing top of the National Division One, taking the place of Leeds Carnegie who were relegated.

Leicester Tigers finished top of the league table, then were crowned Champions after defeating Bath 24–10 in the semi-final and London Irish 10–9 in the final at Twickenham.

The seventh berth was secured by Northampton Saints when they defeated French side Bourgoin in the European Challenge Cup final on 22 May.

Northampton Saints, having won the 2007–08 National Division One, replaced Leeds Carnegie, who were relegated last season after finishing bottom of the table.