Police said Khargeswar Barman(30) hung himself with a cloth in prisoners' barrack number 7 at around 2.45 am.
The body was found hanging from a window during change of duty by a guard, who informed the jail authorities.
The reason for the suicide was not immediately known, the police said.
Barman, who hailed from Noonmati-II village of Dhubri district, was in the jail since September 13 in connection with the murder of his wife in which he was allegedly involved.
He was booked under Sections 302 (guilty for murder), 342 (wrongful confinement), 147 (guilty of rioting) and 148 (wrongful confinement to extort confession) of IPC.