Sonia to lead parliamentary opposition

It marks the first time that Mrs Gandhi will lead her party in parliament, as she had never previously been an MP.

It has also been announced that she will resign from the Bellary parliamentary seat in south India, retaining Amethi in Uttar Pradesh.

She won both seats in the recent general election.

Candidates in India are allowed to contest two seats, but must resign from one within 15 days of the election.

The speaker of the Lok Sabha - the lower house of parliament - will make a formal announcement on Mrs Gandhi's official position when the house meets for its first session on Wednesday.

Family stronghold

The BBC's Daniel Lak in Delhi says Sonia Gandhi's decision to stay on as member of parliament for the Amethi constituency is not unexpected.

The seat is a stronghold of the Gandhi family. Mrs Gandhi's late husband, Rajiv Gandhi, used to represent the seat in parliament, and her mother-in-law, Indira Gandhi, represented a neighbouring constituency.

Sonia Gandhi's move to stand for election from two parliamentary seats led to allegations that she was unsure of winning from Amethi.

It led to the ruling BJP fielding a high-profile candidate to take on Mrs Gandhi in Bellary, in the southern Indian state of Karnataka.

But despite a strong showing by the BJP candidate, Mrs Gandhi won quite easily.

There is some speculation that she might ask one of her two children, both in their twenties, to contest the seat, but the BBC correspondent says that seems unlikely.

Her daughter, Priyanka, campaigned heavily for her in Amethi leading observers to suggest that she was preparing for a future in politics.

Criticism

The recent general election saw the Congress Party go down to its worst-ever defeat.

Sonia Gandhi's political inexperience and her choice of advisors were both heavily criticised during and after the election.

She makes her debut in parliament on Wednesday.

As leader of the opposition, she will be responsible leading her party back to the forefront of Indian politics.

Several controversial economic and social bills are waiting to be taken up for debate, including one on liberalising the heavily-regulated insurance sector and another on setting aside a third of parliamentary seats for women.