Ms Gandhi has been appointed the party general secretary for the eastern part of the crucial state of Uttar Pradesh.
She has campaigned extensively for her brother and mother Sonia Gandhi in earlier elections, but had refused a formal political role for herself.
Analysts say she will infuse fresh energy into the Congress campaign.
The main opposition Congress party was routed by Prime Minister Narendra Modi's Bharatiya Janata Party (BJP) in the last general election in 2014 and has found it hard to recover.
Ms Gandhi has always been considered more popular of the Gandhi siblings with many blaming the "lacklustre leadership" of her brother for a string of Congress defeats between 2014 and 2018.