Kerala Chief Justice Manjula Chellur administered the oath of office to him.
Kerala Chief Minister Oommen Chandy, his cabinet colleagues, Leader of the Opposition in the assembly V S Achuthanandan and senior state government officials were present at the swearing in ceremony.
72-year-old Kumar, a retired IPS officer, had also served as head of the National Security Guard. He was also a former Congress MP .
He succeeds Karnataka Governor H R Bhardwaj who was holding additional charge of the state after the demise of M O H Farooq in January 2012.