Renzaho was born in the Gaseta sector of the Kigarama commune, in the Rwandan prefecture of Kibungo. He was educated as a military engineer in various academies in Germany, France and Belgium. After returning to Rwandan he rose to the rank of colonel in the Rwandan Armed Forces.
In 1990, he entered politics. An ethnic Hutu, he was a part of Juvénal Habyarimana's dominant MRND party. He became governor of the prefecture of Kigali, and president of the Civil Defence Committee for Kigali.
According to the prosecutor for the International Criminal Tribunal for Rwanda, Renzaho is alleged to have contributed to the genocide in numerous ways between 7 April and July 1994, including exercising his authority to set up roadblocks for the interception and murder of Tutsis, dismissing councillors who objected to the genocide, personally ordering the detainment and murder of Tutsis, equipping genocidaires with Kalashnikov rifles, and ordering the murder of the journalist André Kameya.
On July 14, 2009 the U.N. War Crimes Tibunal in Arusha, Tanzania sentenced Renzaho to life in prison. Renzaho's lawyer, Francois Cantier, says he plans to appeal the decision.