If he follows the path of his peers, he could also join the boards of major private and public companies as a non-executive director.
Individuals who have amassed decades of experience working at the so-called Big Four accounting firms including EY, KPMG and PricewaterhouseCoopers (PwC) are among the most sought-after by companies out to tap their knowledge in various areas.
These include tax, audit, human resource, compliance and corporate restructuring.
Mr Onyango’s predecessor Daniel Ndonye was, for instance, appointed to several boards including oil marketer KenolKobil after he retired in 2010.
Charles Muchene, a former executive of PwC in Kenya, has joined several boards including Barclays Bank of Kenya #ticker:BBK and East African Breweries Limited #ticker:EABL where he is chairman.
Mr Onyango’s exit comes as Deloitte marks 110 years of its operations in East Africa.
The incoming CEO, who has been the deputy since June 2006, has more than 25 years of professional experience.