[1][3] Akumu first met Trade Unionist and popular politician, Tom Joseph Mboya in 1952 while both were participants in a debate at the Mbagathi Postal Training Center.
Mboya, who then worked as a Health Inspector at the Nairobi City Council had a massive influence on Akumu's career.
In 1958 Tom Mboya sent Akumu to Accra, Ghana to attend the preparatory committee meeting of the All African People’s Conference where he met President Kwame Nkrumah, a man he greatly admired.
In 1965, Dennis Akumu joined the Central Organization of Trade Unions of Kenya as a Deputy General Secretary.
While attending the All African People’s conference in Tunisia in 1960, due to the polarizing positions at Lancaster House constitutional conference he was airlifted from the Tunisia meeting to London to serve as the so called a “backroom man” to help reach compromise on the type of constitution Kenya would adopt.
In 1969, he was elected Member of Parliament for Nyakach constituency under the one party system of the Kenya African National Union (KANU) and served until 1973.
He was honored to represent the people of Nyakach in Parliament and as Member of Parliament, he worked for and attained improvements for his constituents as is fondly remembered for improving roads, broadening access to piped water, ensuring better health services and facilitating access to higher education through his international networks to the United States, Europe, Asia and across Africa.
Akumu was instrumental in the reburial of President Kwame Nkrumah and the establishment of the WEB Dubois Center in Accra, Ghana.
After a decade-long struggle with kidney failure, he died on 18 August 2016 at the Aga Khan Hospital in Nairobi, age 82.