He died at the age of 88 at Nairobi Hospital while receiving treatment, according to a statement released by his family.
Nyachae was also a successful businessman and entrepreneur with profitable investments inside and outside Kenya.
He was born on February 6, 1932, in Nyaribari, Kisii County, to a powerful colonial chief, Musa Nyandusi.
Nyachae served under the regimes of the late president Daniel arap Moi and retired president Mwai Kibaki. He also served as a provincial administrator in various parts of the country.
Former prime minister Raila Odinga posted on Twitter: “My heartfelt and sincere condolences go out to the family of former cabinet minister, MP and long-serving career civil servant Simeon Nyachae. The Abagusii community has lost one of its most illustrious sons. May he rest In eternal peace.”
CEO of the Kenya Film Classification Board Dr Ezekiel Mutua said Nyachae was “an enigma, an outstanding long-serving top civil servant and an astute leader and businessman who spoke his mind and left a rich legacy of an impeccable service to the nation”.
“Fare ye well, Mzee Nyachae. Your legacy lives on!” Mutua said.
Nyachae had five wives and 20 children. His first wife, Esther, died in August 2016 after a long illness.