Rajdeep garnered 40,090 votes, while Thakur got 30918 votes, election office said.
The seat was held by Rajdeep Goala's father Dinesh Prasad Goala whose death necessitated the by-poll.
Opposition AIUDF President Badruddin Ajmal's son Abdur Rahim Ajmal is leading over Congress' Bashir Uddin Laskar in Jamunamukh.
In Silchar, BJP's Dilip Kumar Paul is ahead of Arun Dutta Majumdar of Congress.