Prior to his appointment as Principal Secretary at the State Department of Livestock in the Kenyan Ministry of Agriculture Livestock and Fisheries in December 2015, Tuimur worked for the Agricultural Development Corporation for nearly 30 years, rising to be Managing Director. His career has spanned the government, private and academic sectors. In addition to his roles at the Agricultural Development Corporation, he was chairman of the National Standards Council (2000–2003). He has served on the Insurance Advisory Board of Directors (1999–2002) and on the board of the Agro-Chemical and Food Company Limited. He has an MSc from the University of Edinburgh, and a BVM from the University of Nairobi. He joined the Board representing the Government of Kenya in February 2016.