While in Canada, he came into contact with many Rwandans who were determined as much as he was to return to Rwanda some day. He soon became deeply involved in the
Rwandese Patriotic Front (RPF) activities, which had been founded to launch a struggle against the then Rwandan government that had denied its citizens the right to return to their
homeland. When the RPF launched an armed war on 1 October 1990 against the Rwandan government, Mazimhaka was appointed RPF's Commissioner for External Relations. On September 15, 1993, he led the RPF delegation to pressure the UN at its headquarters in New York for deployment of peacekeeping troops, which would later go on to form the UNAMIR. He was later elected the vice-chairman of RPF in 1993, a position he held until 1998. Mazimhaka was appointed the Minister of Youth, Sports and Cooperatives in July 1994 soon after the RPF had ousted the regime of
Juvénal Habyarimana in April 1994. He held this position until 1996, when he was made Minister of Rehabilitation and Social Affairs. A year later he was appointed Minister in the Office of the President until 2000 when he was made a Special Envoy of the President. This agreement outlined the disarmament of the former
Rwandan Armed Forces (
Ex-FAR) and the
Interahamwe militia on the one hand, and the withdrawal of Rwandan forces from the
Democratic Republic of Congo (DRC) on the other. He had also previously been involved in negotiations for the formulation and implementation of The
Lusaka Ceasefire Agreement in the DRC, while Minister in 1999. ==Later activity==