The merger, which took place in the presence of Congress chief Sonia Gandhi and vice president Rahul Gandhi, will strengthen the party in Haryana, Congress general secretary Shakeel Ahmed told the media at Parliament House here.
Kuldeep Bishnoi's late father Bhajan Lal, Haryana's former chief minister and one-time strongman of the Congress, floated the Haryana Janhit Congress in 2007 after he broke away from the Congress.
"The Manohar Lal Khattar government's functioning in the state has turned many towards the Congress," Ahmed said.
Speaking on the occasion, HJC leader Kuldeep Bishnoi said his party had merged with the Congress to fight the communal forces in the state.
"We want to eradicate communal forces like the Bharatiya Janata Party from the state," he said.
Former Congress chief minister Bhupinder Singh Hooda said the merger shows that the Congress was gaining in strength and will return to power in Haryana.