He later served as the chief secretary in the civil service under the governments of Jomo Kenyatta and Daniel Arap Moi.
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.
[6] Nyachae's plans to run for the presidency did not receive wide support, as the main opposition groups cooperated with Mwai Kibaki's Democratic Party to form the National Alliance of Kenya, which then teamed up with Raila Odinga's Liberal Democratic Party (LDP) to form the National Rainbow Coalition (NARC).
[6] During the 2002 general elections, Nyachae did not succeed in his presidential bid, but was able to enter parliament with a 14-member Ford–People faction, having won all constituencies in Kisii.
[6] Nyachae was named in the Waki Report as one of the masterminds of the 2007–08 post-election violence in which more than 1,600 people died, as he was believed to have organised attacks on ODM opposition leaders.
The opposition wave swept his Kisii stronghold and he was soundly defeated, as many government ministers and Ford–People candidates running for office were viewed as being tightly linked with him.
Nyachae ran a chain of businesses ranging in nature from agriculture, banking, real estate, transportation and manufacturing.