Early life and education
Nyachae was born into a large polygamous family in Nyaribari, Kisii County, on 6 February 1932 to colonial chief Musa Nyandusi and the late Omongina Pauline Bosibori Nyandusi. In 1941, his father enrolled him in the Nyanchwa Seventh-day Adventist School, and in 1947, he joined the Kereri Intermediate School. Two years later, in 1949, he joined the Kisii Government African School but withdrew in 1953, just a year before he was due to sit for the Ordinary Level School Certificate. He then took up employment at his father's chief's camp as a district clerk. He later attended Torquay Academy and Churchill College, Cambridge, both in the United Kingdom.
Nyachae's career in the civil service began at this point. In 1957, he went to study public administration in London, returning to Kenya in 1960. Upon his return, Nyachae was posted as a district officer in Kangundo Division and later returned to Churchill College, Cambridge for a diploma course in public administration. He became a district commissioner by December 1963. Upon his arrival back in Kenya in 1964, he went back to provincial administration and began to steadily rise up the ranks within the provincial administration, ending up with a position as a provincial commissioner from 1965 to 1979. He later served as the chief secretary in the civil service under the governments of Jomo Kenyatta and Daniel Arap Moi.
Career in politics
Upon his retirement from the civil service, Nyachae was arguably one of the most prominent personalities from Kisii County. He won a parliamentary seat in 1992. His election in Nyaribari Chache Constituency was instrumental in his entry into the Moi government as a cabinet minister first for agriculture and later for finance.
In 1999, he fell out of favor with Moi and resigned from the government after having been moved to the less influential Ministry of Industry. He also left the Kenya African National Union (KANU) to join the opposition, Ford–People, which was by then only a small party with roots in Central Kenya and three deputies in parliament.