Choudhury cited the "directionless and confused leadership of the APCC" as the main reason for leaving in the letter addressed to Congress president Sonia Gandhi.
He said the Congress party in Assam had become "unstable" as a result.
Choudhury further claimed that despite senior party leaders' public acknowledgement of the fact that Congress MLAs had cross-voted in the most recent presidential elections, he and other party workers felt demoralised.
He mentioned that the president of Assam Congress Bhupen Bora was aware of the issue of MLAs who cross-voted and had referred to them as "gaddar" (cowards).
Meanwhile, he continued, "thousands of grass-root workers like me” have contributed “blood and sweat for the party for years."
It may be noted that earlier Choudhury was the president of the Assam Pradesh Youth Congress (APYC) and National Secretary of the Congress' student wing, the National Student Union of India (NSUI).