No one else submitted nomination papers for the role by Monday's deadline. Gandhi's promotion to leader of the Indian National Congress, or Congress party, was long expected and comes as the party is at a nadir in its fortunes, losing a series of state elections and struggling to counter Modi's widespread popularity and his upbeat message of development and economic prosperity for all.
Gandhi, 47, a three-time member of Parliament, is the descendant of towering figures in Indian history, including his grandmother, Indira Gandhi, and his great grandfather, Jawaharlal Nehru, who helped lead the country's independence movement from Britain.
Prime Minister Narendra Modi who is currently campaigning in state elections in his home state of Gujarat against the Gandhi's party took a dig at the expected victory, comparing the Gandhi dynasty to Muslim Mughal kings of the past.
"When Shahjahan came after Jahangir or Aurangzeb came after Shahjahan, were there any elections for that?" he said.
"I congratulate the Congress on their 'Aurangzeb Raj,'" he added, comparing Gandhi to the widely unpopular historical king.
Gandhi, dubbed "the Reluctant Prince" by the Indian media, has long appeared to be ambivalent about his family's business, and critics have charged that he is effete and out of touch, despite leading a party that has historically championed India's poor and found its strength in its villages. In 2014, he led the Congress party's campaign in the national election where the party won just 44 seats in the lower house of Parliament, the worst showing in its history.
Gandhi briefly disappeared from the scene in 2015 - where he reportedly attended a meditation retreat to contemplate his future - and has appeared re-energized in recent months, analysts say, touring colleges, criticizing Modi with new vigor and hiring new staff to beef up his presence on social media.
"People are talking him more seriously now," said Sudha Pai, a fellow at the Indian Council of Social Science Research. "He has played a more sustained role in politics and has not disappeared in between or kept quiet - that was his style earlier. He was seen as a very reluctant politician."
As a child, Gandhi lived a fairly sheltered existence in New Delhi, especially after his father, Rajiv, who served as prime minister from 1984 to 1989, was assassinated by a Sri Lankan separatist in 1991. He went on to graduate from Cambridge University and work as a management consultant before winning his father's old parliament seat in 2004.
He declined to serve in a cabinet post during his party's decade-long tenure, leaving himself open to criticism that he has no administrative experience, according to Shekhar Gupta, a columnist and editor in chief of the news website ThePrint.
"Rahul has never had any responsibility," Gupta said. "My own view is that he's been pampered too long and allowed himself to be protected for too long. Now he's out there and his neck's on the line."
Gandhi will replace his mother, Sonia, as party president. Italian-born Sonia Gandhi, now 70, was a powerful leader in her own right, serving 19 years as party president after the death of her husband and led the party to two national general election victories, in 2004 and 2009.
Modi's Bharatiya Janata Party sees Gandhi's appointment as a positive, analysts say, because they can continue to target him as the spoiled child of a fading dynasty who has no acumen for politics.
"I don't think he has matured in the sense that he can stand up and say 'I am my own man and I take my own decisions for better or worse,'" said Kanchan Gupta, a journalist and political analyst. "Unfortunately the Congress has internalized the fact that only a dynast can lead the party."
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