Sonia Gandhi, the president of the Congress party in India, is back at work after undergoing surgery abroad for an undisclosed medical condition.
Mrs Gandhi chaired a meeting of the party's election committee on Thursday to finalise candidates for the upcoming elections in Uttar Pradesh state.
Mrs Gandhi, 64, is seen as a key decision-maker in the government.
Correspondents say the government faced serious problems during her month-long absence.
Prime Minister Manmohan Singh was severely criticised for mishandling anti-corruption protests in August by activist Anna Hazare.
Many commentators said that Mrs Gandhi would have handled the situation better if she had been in Delhi.
Mrs Gandhi is the widow of former Prime Minister Rajiv Gandhi.
The BBC reports she had named a four-member team to run party affairs during her absence. The team included her son and Rahul Gandhi MP, who is tipped as a future prime minister.
The Nehru-Gandhi dynasty has ruled India for most of the time since Independence in 1947.