District and Sessions Court Judge Ashok Menon also convicted his mother Rajamal under IPC section 498 (cruelty to women) in the case.
The quantum of punishment would be announced on Saturday.
According to prosecution, Biju gave liquor to his wife, Reshmi and made her unconscious, and later strangulated her to death.
She was found dead at her house in Kottarakkara on February 4, 2006.
During investigation it was proved to be a a case of murder. Also, Radhakrishnan's son had deposed against him.
Also Read
Radhakrishnan, now in prison in connection with murder and solar scam cases, had cheated many people of lakhs of rupees along with Saritha after promising solar energy solutions.
The solar scam came into the limelight in June last year after three staff members of Chief Minister Oommen Chandy's office were found to have links with Saritha.
It was during the investigation of the solar scam that police found that Reshmi's death was a case of murder.