Rampaul played youth cricket for West Indies and Trinidad and Tobago, playing at the World Under-15 Challenge in England in 2000, and at the 2002 Under-19 World Cup, before breaking the record wicket tally in the regional youth tournament in West Indies after taking 45 wickets in five matches during the 2002 tournament. The following season, he took 27 wickets, as Trinidad and Tobago won their first youth title since 1987. By that time, however, he had also made his first-class debut, playing three Busta Cup matches for Trinidad and Tobago during the 2001–02 season and taking six wickets.

After playing six further matches during the 2002–03 season, and taking 18 wickets, with only Marlon Black taking more for Trinidad and Tobago that season, Rampaul was selected for West Indies Under-19s in the 2003-04 Red Stripe Bowl one-day tournament. Rampaul was leading wicket-taker for the U-19 team, as his eight wickets was double that of any other, and after the tournament completed, Rampaul was called up to represent West Indies in their tour of Zimbabwe in October and November.

Rampaul went wicketless in his first game, sending down 13 no-balls in 30 overs, and was not selected for either of the two Test matches. However, after taking two wickets, including opener Dion Ebrahim, in the one-day warm-up match against Zimbabwe A, Rampaul played in four of the five ODIs. He failed to take a wicket in the series, which West Indies eventually claimed 3–2 with a win in the final game, and Rampaul was the most expensive West Indian bowler among those bowling more than four overs per game,

Rampaul also went to the South African leg of the tour, and recorded his first five-wicket-haul in first-class cricket, taking five of the first six wickets in a tour match against Free State. They were 86 for six after West Indies had posted 618, and Rampaul ended with figures of five for 55. Rampaul played all three tour games, but once again was left out of the Test matches. After "impressing" in a one-day tour match against South Africa A, he was left out of the team for the first ODI, but replaced Vasbert Drakes for the second match after West Indies had lost the first by 209 runs. Rampaul picked up the wicket of Jacques Kallis for 16, and contributed 24 runs, his highest ODI total to date, but was last out as West Indies lost by 16 runs. He removed Kallis again in the final ODI, when West Indies had a chance to level the 5-match series to 2–2 (with one match rained off), but Kallis had already made his best ODI score to date, scoring 135 as South Africa chased the West Indian total of 304 for two. Rampaul's ten overs cost 56 runs, but he was praised for a "marvellous late effort"

After once again playing in the Under-19 World Cup, taking nine wickets as West Indies reached the final but ultimately lost to Pakistan, Rampaul played in all five ODIs against England at home, taking four wickets but once again being the most expensiv