James Mathew, a member of the CPI (M) state committee, surrendered at Sreekandapuram police station in Kannur district. The first-time MLA from Thaliparamba was arrested after the police recorded his statement.
The High Court had earlier rejected his anticipatory bail in the suicide case.
Another person, M V Shaji, had already surrendered before police on February 17 in connection with the case.
E P Sasidharan, Headmaster of Tagore Vidhya Niketan Higher Secondary School at Thaliparamba, committed suicide by hanging himself at a lodge in Kasargod, police said. He left a suicide note accusing M V Shaji and Mathew of harassing him over administration of the school and forcing him to take the extreme step, police said.
Dismissing their anticipatory bail pleas, the court had said on February 12 their custodial interrogation was necessary.