The celebrations began as party workers danced outside the office with drum rolls.
Congress, earlier in the day, held a celebration and distributed sweets at party's headquarters in the capital.
Rahul, who was elected unopposed as the Congress president on Monday, will formally take over the post on Saturday.
Stall selling badges and key chains with Rahul's photos were also set up outside the party headquarters.
The Congress Party is also set to organise a grand celebration in the national capital.