As a believer in the potential of the African continent, Humphrey is credited with creating some of the most successful businesses in Africa within the Power, Hospitality and Real Estate sectors.​

He began his entrepreneurial career in the early 1980s after working with the Central Bank of Kenya. His initial ventures included Nairobi’s famous Green Corner restaurant, which is quoted on President Obama's list of most visited sites in Nairobi, and the Twigs Restaurant and Cactus Bar.​​

Building unparalleled standards in the region for its work ethic and operation quality has been a priority for Humphrey. This is anchored in the business’ values of excellence, ambition, ethics, sustainability and responsibility. The success of his businesses is shared with the communities in which they operate, across education, health, development and environmental conservation.​

Throughout his tenure at JCG, and continued in his private life, Humphrey believes African development and long-term structural growth is dependent on access to reliable and affordable energy solutions. He has advocated for finding localised solutions through enterprise and partnerships, working towards off-grid power solutions and continued investments in renewable energy solutions. ​

An advocate of wildlife conservation, he supports the Mount Kenya Wildlife Conservancy whose flagship project is the rehabilitation of the endangered Mountain Bongo antelope.​

Humphrey is the Founder and Patron of Humphrey Kariuki Foundation.​