He said the results were a big step towards Congress-free India. He also said the results have formed a strong foundation for 2019 general elections.
The party leadership also thanked the people of Assam and credited the victory there and increased vote share in other states to party workers, state leaders and Prime Minister Narendra Modi.
"BJP's performance in assembly polls is in a way people's stamp on performance of Modi government in the last two years. Poll results show that a strong foundation of BJP has been laid for ensuring victory in 2019 Lok Sabha polls.
"The verdict is a lesson for Congress for its obstructionist politics in Parliament," BJP President Amit Shah said at a press conference here.
He congratulated the Prime Minister, chief ministerial candidate Sarbananda Sonowal and Himanta Biswa Sharma and other leaders and workers for the Assam victory and praised the hard work of leaders in states like Kerala, West Bengal and Tamil Nadu.
"The unmatched efforts and sacrifice of our workers in Kerala, West Bengal and Tamil Nadu have established a strong party base in these states. Congratulations to workers and leaders of West Bengal, Tamil Nadu, Kerala and Puducherry for their hardwork leading to excellent results," he said.
He also congratulated workers and leaders of Gujarat for winning the Talala Assembly bypoll. The seat has been wrested from Congress.
Union Minister Sushma Swaraj said the Assam poll victory is a result of lifetime work of workers and leaders in building the organisation.
"My heartfelt gratitude to the people of Assam for electing a BJP Government in the state. Profound greetings to the BJP workers of Assam.
"This victory is the result of life time work of those who dedicated their lives building the organisation in the north east. My greetings to BJP President Amit Shah and Prime Minister Narendra Modi," she said.
Union Minister M Venkaiah Naidu said BJP's victory in Assam is a "happy gift" to the party and the Prime Minister on completion of two years of NDA government at the Centre.
"Today's result is a clear slap on the face of opportunistic opposition alliance. Assembly results clearly show that people of India are intolerant towards Congress party because Congress was not ready to accept the verdict of the people," he told reporters.
BJP leader Murli Manohar Joshi, who is part of party's Margdarshak Mandal and was among the veterans who were critical of Modi-Shah leadership after the Bihar debacle last year, has written to both the PM and the party chief, congratulating them for BJP's success in these polls.
He voiced hope that it will give the workers confidence to replicate the same in the upcoming elections, especially in Uttar Pradesh.
The Bharatiya Janata Party (BJP) were leading in Assam on 89 seats, way ahead than Congress that was tottering at 21 seats.
The party was winning on 3 seats in West Bengal. The party has, however, got better vote share, said Amit Shah. In Kerala, the party winning a seat.