He was the Minister of Urban Development and Municipal Affairs in the Government of West Bengal for three consecutive terms (1996–2011).
He was elected to the West Bengal Legislative Assembly from Siliguri (Vidhan Sabha constituency) as a CPI(M) candidate for the first time in 1991.
In 2011 West Bengal Legislative Assembly election, he was defeated by AITC candidate Rudra Nath Bhattacharya in Siliguri.
But he won from Siliguri again in 2016 West Bengal Legislative Assembly election against AITC candidate and former captain of India national football team Bhaichung Bhutia.
Ashok Bhattachrya lost the Siliguri corporation election 2021 by Md Alam Khan of TMC from ward number 6.