The 26-year-old made his Irish Schools debut against Scotland at Thomond Park (April 1998) in a starting XV that included Paul O'Connell. He won his fourth Schools cap in December of that year alongside Denis Leamy in the game against the touring Australian Schools side. Lewis made his Under-21 international debut as a replacement in the Five Nations opener against England at Banbury RFC in February 2000, in the company of current Munster squad members, Donncha O'Callaghan, Paul O'Connell, Frank Roche and Mossie Lawlor.
In June 2001 he wore the number 13 jersey in all of Ireland's U-21 World Cup games in Australia, in the final game partnering Lawlor in Ireland's 43-42 victory over South Africa at Sydney Showground.
Speaking about his move south, Lewis said: "Of course I am looking forward to it. Its a challenge I'm looking forward to. They (Munster) are a great side and I believe this is a good opportunity for me. I know a lot of the Munster lads after been involved with them at various levels so I think I know what's required.
"Yes there are regrets to be leaving Leinster. I've been here right from the start, have enjoyed my time and learned a lot here. I hope to help them achieve a few things before the end of the season."