She had taken over the leadership in challenging circumstances in 1998 and now as interim chief, she faces a perhaps even tougher task with Congress having lost two successive Lok Sabha elections is facing resignations of party leaders across states as well as battling some apparent ideological confusion.
Rahul Gandhi was also a key face of the party in the 2014 elections.
In the past five years, BJP has considerably expanded its base and won states it had never won in the past and emerged as the principal pole of national politics replacing the Congress.
Apart from the long term challenges in states such as Uttar Pradesh and Bihar, where the party has gone weak, the immediate task before Sonia Gandhi will be to put up strong challenges in election-bound states of Maharashtra, Jharkhand, and Haryana.
The Central government has taken a momentous decision to repeal Article 370 and bifurcate Jammu and Kashmir into two union territories and Sonia Gandhi will have to guide the party through the change and decide its political strategy.
Some party leaders have already differed with the party's official view on the issue.
The Centre is also keen on early assembly elections in Jammu and Kashmir. Sonia Gandhi is into her fifth term as Lok Sabha MP. She will be interim chief pending the election of a regular President by the AICC.
She commands respect, trust, and loyalty of party leaders workers across the generational divide and that is expected to help in taking any tough decisions.
Sonia Gandhi was a reluctant entrant into politics and became party chief in 1998 a year after she became a primary member of the party and continued in the post till 2017.
She resigned apparently over health concerns as also to herald a generational change in the party. She made mistakes at the beginning of her political innings but learned from them quickly.
She improved her grasp over Hindi, the language of politics in vast parts of the country and delivered hard-hitting speeches that made her opponents sit up and take notice.
The issue of her foreign origins was raised by Sharad Pawar, Tariq Anwar and PA Sangma which led to their expulsion and she kept the party united.
While Anwar is now back in Congress, Pawar is an ally of Congress. Her even-handed approach endeared her to party leaders and workers.
Gandhi stitched coalitions ahead of the 2004 Lok Sabha elections and ousted the Atal Bihari Vajpayee government which was confident of its victory.
The Congress-led UPA of which she is the chairperson won another term in office in 2009. She did not accept the post of prime minister in 2004 and worked for a rights-based agenda in UPA governments. Sonia Gandhi married Rajiv Gandhi, son of then Prime Minister Indira Gandhi in 1968.
Born on December 9, 1946, in a village Lusiana in Italy, she attended a foreign language school.
She spent most of her married life largely as a private citizen looking after her family. When Rajiv Gandhi became Prime Minister in 1984, she accompanied him on some of his tours. She also looked after his parliamentary constituency.
After Rajiv Gandhi`s assassination in 1991, there were demands for her to assume political roles. She resigned from Lok Sabha seat in 2006 as also the chairperson of the National Advisory Committee after a controversy over the office of profit issue and was re-elected.
Her interests include reading, Indian art, handloom and handicrafts, and classical music.
Sonia Gandhi, 72, was the chief when the Congress received its worst drubbing in a Lok Sabha election and won 44 seats.