Speculation heightened in January 2004 about his and his sister's possible entry into politics when they visited their father's former constituency of Amethi, which their mother held at the time. He refused to give a definitive response, stating "I am not averse to politics. I have not decided when I will enter politics and indeed, if I ever will." In March 2004, he announced his entry into politics by declaring his intention to contest the May 2004 elections, standing from Amethi.

At the time, this move generated surprise among political commentators, who had regarded his sister Priyanka as being the more charismatic and likely to succeed. Party officials did not have curriculum vitae ready for the media, such was the surprise of his move. It generated speculation that the presence of a young member of India's most famous political family would reinvigorate the Congress party's political fortunes among India's youthful population.

In his first interview with foreign media, he portrayed himself as a uniter of the country and condemned "divisive" politics in India, saying that he would try to reduce caste and religious tensions. His candidacy was greeted with excitement by locals, who had a long standing affinity with the family's presence in the area. He won with a landslide majority, retaining the family stronghold with a huge margin as the Congress unexpectedly defeated the ruling Bharatiya Janata Party. His campaign was masterminded by his younger sister, Priyanka.

Rahul was once again at his mother's side when she announced her resignation from the Lok Sabha and also as chairperson of the National Advisory Council on March 23, 2006, under the office-of-profit controversy. Sonia then vowed to seek a fresh mandate in Rae Bareli, which sent her to power in 2004. She was re-elected in May 2006 by a huge margin of over 400,000 votes.
Since his entry into active politics, Rahul has shown a special interest in the resurgence of the Congress Party in Uttar Pradesh. He was a prominent figure in a high profile Congress campaign for the 2007 Uttar Pradesh Assembly elections. Although the Congress won only 22 seats with 8.53% of votes, Rahul became firmly established as the next big hope of the party.

Rahul was appointed a general secretary of the All India Congress Committee on September 24, 2007 in a reshuffle of the party secretariat. In the same reshuffle, he was also given charge of the Youth Congress and the National Students Union of India.

Rahul is also seen as the chief architect of the Congress Party's resounding victory in the 2009 Lok Sabha elections. He retained his Amethi constituency by defeating his nearest rival by a margin of over 333,000 votes. In these elections the Congress is said to have revived itself in Uttar Pradesh by winning 21 out of the total 80 Lok Sabha seats and the majority of the credit for this turnaround is given to Rahul Gandhi. He spoke at 125 rallies across the country in six weeks