Superintendent of the correctional home, Madhusudan Sarkar, said Ramshankar Basak took a shaving blade and tried to slash his own throat with it.
A barber brought the blade to shave Basak, who was arrested on January 29.
Basak was admitted at Jalpaiguri hospital and he was out of danger, Sarkar said adding probably the KLO linkman was suffering from depression as he failed to secure bail.
There would be an investigation into the incident, he said.
Basak was arrested from near the Indo-Nepal border in Darjeeling district along with two senior KLO leaders who were allegedly involved in a bicycle blast on December 26 last year in Jalpaiguri that left six persons dead.
Formed in 1993, the KLO was fighting for a separate Kamtapuri state comprising six districts of north Bengal and some areas of Lower Assam.