Joseph Kanyabashi was born in Mpare, in the prefecture of Butare, Rwanda, in 1937. He was mayor of the commune of Ngoma, in Butare, from April 1974 until the day he left Rwanda, which was on or around 4 July 1994. In his capacity as mayor, he was the highest representative of the executive power at a communal level. He exercised authority over all his subordinates and could requisition the local police units.
From the end of 1990 to July 1994, Kanyabashi was said to have participated in the elaboration of a plan to eliminate Tutsis.
On different occasions between April and June 1994, Kanyabashi was said to have encouraged the population to eliminate all Tutsis in the province of Butare. On 19 April 1994, he reportedly made a speech in Butare, in which he appealed to the audience to rise up against the Tutsis. Shortly thereafter, indiscriminate large-scale attacks against Tutsis occurred in the region. Towards the end of May 1994, Kanyabashi allegedly drove through the city of Butare in a car, calling upon the civilian population to track down the Tutsis. Around the same time, he allegedly organized two gatherings in Cyarwa, in the community of Ngoma, during which he encouraged the inhabitants to kill Tutsis.
Before and during the massacres of 1994 in Butare, Kanyabashi is said to have distributed arms to the militia and certain civilians with the aim of exterminating the Tutsi population and the moderate Hutus. Between March and June 1994, he allegedly helped with and facilitated the military training of militia units from the commune of Ngoma.
On 21 and 22 April 1994, Tutsis fleeing the massacres went to the village of Kabakobwa, after allegedly having been promised by Kanyabashi that he would protect them there. He was said instead to have ordered his subordinates, and encouraged Hutu civilians, to eliminate the Tutsis that had sought refuge there. Around 4pm on 22 April 1994, his subordinates, aided by Hutu peasants and the militia, attacked the refugees. During the attack, Kanyabashi reportedly called up members of the presidential guards as reinforcements and on arrival they also participated in the killings.
Towards the end of April 1994, Kanyabashi allegedly escorted two busloads of Tutsis, all of whom had sought refuge in the prefectural buildings, to the Rango forest accompanied by members of the local police. Upon their arrival, the Tutsi refugees were detained in a fenced enclosure. During the ensuing weeks, the refugees were deprived of food and subjected to beatings. Several died but others were rescued in early July 1994 on the arrival of the Rwandan Patriotic Front (RPF) (an opposition movement almost entirely composed of Tutsi refugees and led by Paul Kagame).
Around that period of time, Tutsis fleeing the massacres had gathered in the Matyazo clinic in Ngoma commune in order to seek refuge. Kanyabashi was said to have gone there and demanded them to stay put for their own safety. Nevertheless, shortly thereafter Kanyabashi allegedly ordered the soldiers to open fire on these refugees. Several Tutsis were killed in the shootings.
In that same period, Kanyabashi reportedly held a reunion in the parish of Ngoma in order to assure the civilians that there would be no further massacres. Many Tutsis had sought refuge in the parish in trying to escape the massacres, including among them survivors of the attack on the Matyazo clinic. On the morning of 30 April 1994, a group of armed soldiers and numerous Interahamwe (an extremist Hutu militia) came to the parish church of Ngoma and ordered the refugees out of the church, telling them that they would be taken to a nearby camp-site where they would be safe. However, on the way, they were attacked and massacred by the Interahamwe in a sports field, just adjacent to the parish.
In early May 1994, Tutsis from the region of Mare, who had sought refuge in the University Hospital of Butare, were fearful of returning to their region. Kanyabashi, who was present at the hospital, allegedly promised to protect them and to provide them with a military escort to accompany them safely back to their homes. Kanyabashi reportedly left the hospital first at the head of a long line of refugees, who were subsequently slaughtered instead of being accompanied back to their homes. On 15 May 1994, Kanyabashi and members of the military were said to have checked the identity cards of patients in the Butare hospital in order to identify who were the Tutsis. Those selected were then allegedly taken away by the military in the presence of Kanyabashi, following which they were killed.
Between mid May and mid June 1994, Kanyabashi and Sylvain Nsabimana, the préfet of Butare, ordered that Tutsis, who had sought refuge in the Butare prefectural building, be transported to Nyaruhengeri commune and specifically to Nyange. During that trip, they were attacked by armed groups and many of them were killed. Many of those who escaped returned to the prefectural building in Butare. During the weeks that followed, Kanyabashi and the military allegedly selected certain refugees and led them by force to the woods neighbouring the Evangelic School of Rwanda. They were never seen again. During a June 1994 meeting in the prefectural offices between some of the main authorities of the prefecture and their subordinates, Kanyabashi reportedly told the préfet, that all Tutsis remaining in the office building should be exterminated.
On or around 4 July 1994, confronted with the approaching troops of the FPR, Kanyabashi fled from Rwanda. On 28 June 1995 he was arrested in Belgium.