"It was not an easy task. But it was made possible due to your support and the love and affection of the grass root and ordinary workers which made the task easier and the credit goes to them", the 66-year-old party chief told the leaders.
Mrs Gandhi is currently in the fourth term of the Presidentship which expires in 2015. Changes have been made in the party constitution that now mandates organizational polls after five years instead of three years earlier.
She has created history by becoming the longest serving chief of the 127-year-old organisation.
Congress leaders said that some Pradesh Congress Committee chiefs had sought permission for celebrating the occasion in a big way, but Mrs Gandhi advised them against it in view of drought situation in some parts of the country.
The highpoint of her political career was in May 2004 when she successfully led the Congress regain power at the Centre, albeit on a coalition platform.
However, in a dramatic turn of events she declined prime ministership and nominated economist-turned-politician Manmohan Singh to the top political post.
She took over the reins of the organisation in March 1998 in the wake of the party's dismal showing in the Lok Sabha polls earlier. The defeat led to the exit of the late Sitaram Kesri from the post of Congress President.
It was then a demoralised and fragmented Congress party was going through a turbulent phase and ruling just a few states.
Several senior Congress leaders including Union Minister Kapil Sibal, Delhi Chief Minister Sheila Dikshit, Minister of State for Planning Rajeev Shukla, Delhi Congress Chief JP Agarwal went to her residence to congratulate her.
"We thanked her for leading the party and strengthening it. Her contribution for the party is worth a praise. Everyone has praised her. All the MPs, MLAs and Ministers have praised her efforts and for leading the party in tough times,"
Mr Shukla told reporters outside Mrs Gandhi's residence.
Praising her leadership abilities, Mr Agarwal said Congress party's future is secure in her hands. "She has amazing leadership quality and ability to tackle problems. Her heart beats for common man and she wants to see everyone happy. So our future is secure with her," he said.
Congress' SC/ST Cell Chairman V Hanumanth Rao expressed confidence that party will come back to power in 2014 General Elections.
"Under her guidance UPA-I and II came in power. I promise that under her leadership Congress will go for a hat-trick in 2014. Her style of functioning is very good and she has said that no injustice will be done with the workers," he said.