The Cork-born whistler is the tournament's most-capped referee and took charge of last year's final between London Wasps and Leicester Tigers, which was also at Twickenham.
On Saturday Lewis will be backed by an all-Irish officiating team as George Clancy and Peter Fitzgibbon will be the touch judges, Brian Fitzgerald is down for television match official duty and John West has been chosen as the citing commissioner.
The nominated referees are drawn from the Heineken Cup 2007/2008 referees' panel.
The nominations are submitted to the ERC Match Officials Sub Committee, made up of Referee Managers from the six Unions of the participating teams, who review and confirm the final appointments.
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