India's main opposition Congress party on Wednesday elected 80-year-old Mallikarjun Kharge as its first non-Gandhi president in over 24 years.

Kharge, considered close to the Gandhi family, defeated a relatively young Shashi Tharoor, a former UN diplomat, by a huge margin.

"Of the over 9,000 votes cast in the party's internal election held on Monday, Kharge bagged nearly 8,000," a spokesperson for the party told the media in Delhi.

Kharge will take over the reins of the grand old party from interim Congress president Sonia Gandhi soon.

After the results were announced at 2pm (local time), former Congress chief Rahul Gandhi congratulated Kharge. "Congress president is the supreme authority," he said.

Earlier in the day, Tharoor alleged "extremely serious irregularities" in the party's internal election process.

The Congress held the election on Monday, where 96% of the 9,915 eligible Congress delegates, representing all Indian states and Union territories, cast their votes.

While Kharge is a staunch Gandhi family loyalist with 50 years of political experience, 66-year-old Tharoor is an articulate leader who joined the party in 2009 after nearly a 30-year stint in the UN.

A PhD from the Fletcher School of Law and Diplomacy, Tharoor served as India's junior Foreign Minister when the Congress was in power from 2004-2014.

Since Prime Minister Narendra Modi's nationalist BJP swept to power in 2014, the Congress has witnessed a vertiginous decline. The Congress is now in power only in a handful of Indian states.

Often blamed for the party's poor performance, Sonia's son Rahul has refused to take over the reins of the party in the run-up to the general elections slated for 2024.