The CS died at Karen Hospital, a few hours after he was admitted for a medical check up.
Head of the Public Service and chief of staff Mr Joseph Kinyua confirmed the sad news in a statement early on Saturday morning.
Sources privy to Mr Nkaissery said he went to Hospital after leaving Uhuru Park where he accompanied President Uhuru at a prayer meeting that was attended by various political leaders.
“He looked okay but he said he needed to go to hospital as he was feeling unwell,” the source said.
Nkaissery has and still is being celebrated as one of unshaken cabinet secretary. In various condolences messages flowing in various social media platforms describe him as loving and a no nonsense man.
Nkaissery was aged 67 at the time of his death.