The bypolls were necessitated after Chief Minister Yogi Adityanath and Deputy Chief Minister Keshav Prasad Maurya vacated the Gorakhpur and Phulpur seats respectively, following their election to the Uttar Pradesh Legislative Council.
"The BJP candidate will taste defeat in Gorakhpur bypolls and it will be the beginning of decline of saffron forces in the country," Mr Chowdhury said in a press meet yesterday.
The results of Gorakhpur will be astonishing and the SP will demolish BJP's ", he said adding that BJP has "reached its peak and now its the time for its decline".
"SP candidate will win in Gorakhpur and our victory has become certain after the support from the BSP," he added.
On possibility of an alliance with the BSP in the Lok Sabha polls, Mr Chowdhury said, "a start has been made. Decision in this regard will be taken by Akhilesh Yadav and Mayawati".
For the BJP, Gorakhpur is significant as it is the bastion of Chief Minister Yogi Adityanath, who has represented the seat in the Lok Sabha five times.