Gambhir was selected in 2000 for the first intake of the National Cricket Academy in Bangalore. He made his ODI debut against Bangladesh in the TVS Cup in 2003. In his third match, he scored 71 and was named Man of the Match. His maiden century {103 off 97 balls) came against Sri Lanka in 2005. In 2004, he made his Test debut against Australia in the fourth and last Test match of the Border Gavaskar Trophy but did himself no favours by getting out for 3 and 1. He made amends in his second Test, however, scoring 96 against the South Africans. His maiden Test century came against Bangladesh in December 2004. Gambhir then made a number of starts in the home series against Pakistan in 2005, but was able to make only one half-century in six innings. He made 97 in Zimbabwe later that year, but failed to reach 30 against Sri Lanka at home, repeatedly struggling against Chaminda Vaas, and was subsequently dropped from the Test team. He was replaced in Tests by Wasim Jaffer, who made a double hundred and a hundred in seven Tests. He has often been criticized as not being able to convert his starts of 20 and 30 into larger scores and his string of poor scores is continually cited as evidence for this assertion.

While he has been out of the Test team, he has played a number of One Day Internationals for India between 2005 and 2007. However, he was not selected for the 2007 Cricket World Cup as the selectors opted for a top-order of Sourav Ganguly, Virender Sehwag, and Sachin Tendulkar. After India's first-round exit from the tournament, Gambhir was selected for the One Day International on India's 2007 tour of Bangladesh. Gambhir scored his second century on that tour and was subsequently selected for the One Day International on India's tour to Ireland in 2007. He scored an unbeaten 80 against Ireland in the first game of that tour and was awarded the man of the match award for that effort. In the post-match interview, he indicated that performing more consistently was a top priority for his career as he had done so in the past. If he does become more consistent, he could cement his place as a One Day International opener in the Indian cricket team.