Prime Minister Narendra Modi's chief rival Rahul Gandhi was nominated on Saturday to lead India's opposition in parliament after an election result that rescued his party from the political wilderness.

Modi will be sworn into office for a third term this weekend following a poll that deprived his ruling Bharatiya Janata Party (BJP) of a majority, forcing it to rely on coalition allies to govern.

Gandhi defied analysts' expectations and exit polls to help his Congress party nearly double its parliamentary numbers, its best result since Modi was swept to power a decade ago.

A meeting of the Congress leadership on Saturday voted unanimously to recommend Gandhi's election as India's official opposition leader, a post that had been left vacant since 2014.

"All participants unanimously passed the resolution that Rahul Gandhi should take the position of leader of opposition in the parliament," K.C. Venugopal told a press conference after a meeting of the party's executive.

The nomination will be put before a meeting of the 232 lawmakers belonging to a Congress-led opposition alliance later on Saturday.

Gandhi is the scion of the dynasty that dominated Indian politics for decades and is the son, grandson and great-grandson of former prime ministers, beginning with independence leader Jawaharlal Nehru.