The meeting was attended by the party's 52 newly elected Lok Sabha MPs and Rajya Sabha members.
Gandhi, who represents Uttar Pradesh's Rae Bareli in Lok Sabha, is the chairperson of the Congress-led United Progressive Alliance (UPA).
"Smt. Sonia Gandhi elected as the leader of Congress Parliamentary Party! She says, 'we thank the 12.13 Cr voters for reposing faith in the Congress Party'," Congress's chief spokesperson Randeep Surjewala tweeted.
The MPs will also elect the Congress leader in Lok Sabha and chalk out the party's strategy for the upcoming session of Parliament, they said.
This will be the first official meeting that Congress president Rahul Gandhi will attend after the May 25 meeting of the party's working committee, where he had offered to quit as Congress chief.
The CWC has already rejected his offer to resign and unanimously passed a resolution authorising him to bring structural changes in the party at all levels in a bid to revamp it.