Ms Koimett is the Principal Secretary for Broadcasting and Telecommunications. She has previously worked as Principal Secretary State Department of Transport. Prior to that she was an investment banker and worked as the Director General Public Investment and Portfolio Management at the National Treasury,  previously served as the managing director and chief executive officer of the Kenya Post Office Savings Bank. Her long career in public service exceeds 25 years in length and  involved service as the Permanent Secretary in the Ministry of Tourism and Information. For at least 18 of those years, she has been involved in investment promotion, public enterprise reform and privatization. She is responsible for the divestiture of parastatal companies either through the selection of a "strategic investor", or through the flotation of an IPO, on the Nairobi Stock Exchange. Some of the privatized companies through this process, include Kenya Reinsurance Corporation, Tourism Promotion Services, Kenya Railways Corporation, Kenya Airways, Kenya Commercial Bank Group, Housing Finance Group of Kenya, Mumias Sugar Company Limited, Kenya Electricity Generating Company and Safaricom.

She is the first-born to the late Moi-era politician Nicholas Biwott. She holds a Bachelor of Commerce (BCom) degree and a Master of Business Administration (MBA) degree, both from the University of Nairobi.