According to Prof Larry Gumbe, a close friend of the deceased, Oloo passed on last night while being rushed to Yala Hospital.
Born David Onyango Oloo, the activist dropped the Christain name and was often confused with Kisumu County Speaker Onyango Oloo who also dropped his christian name (George).
The late Oloo was among university students arrested in the aftermath of the 1982 coup.
He was tortured at the dreaded Nyayo Torture Chambers before serving five years at Kamiti Maximum Prison as a political detainee.
After his release, he fledt to exile in Tanzania and later to Canada where he lived for several years before returning to become involved in politics.
Oloo served as an official of the Social Democratic Party - before becoming a writer and activist - particularly through the political discussion blog, Jukwaa Proboards.
He has been a long-time close ally of activist Miguna Miguna who recently honored him with fifteen copies of his book, Treason.
"We are pleased to announce that Kenya's patriot and former political prisoner Onyango Oloo has been awarded 15 copies of TREASON for his life -long revolutionary contributions," Miguna had announced last week.
Gumbe said Oloo had traveled to Nakuru to receive the books when he fell ill.