The southern African country suffered months of deadly unrest following last year’s disputed elections, when Mugabe failed to win a majority for the first time since independence in 1980.
He and his one-time rival, Prime Minister Morgan Tsvangirai, formed a unity government in February but the premier’s Movement for Democratic Change (MDC) party has reported ongoing attacks.
"There are still reported cases of political violence and this must stop," Mugabe said in a Harare hotel, standing alongside Tsvangirai for only the second time since the government was formed.
"Let us move among the people… promoting the values and practice of tolerance, respect, non-violence and dialogue as a sustainable means of resolving political differences," Mugabe said.
About 200 lawmakers, government officials and diplomats attended the two-hour event to officially begin three days of national prayer for peace.
Although no organised events have yet been announced for the weekend, Tsvangirai said the event marked the start of efforts to find justice for victims of the violence.
"These three days of dedication must herald the beginning of a genuine, open and frank process… accepting responsibilities for the hurts and pains inflicted on so many Zimbabweans," he said.
"In addition to the three principles of truth, justice and forgiveness, we must openly discuss the issue of reparation," Tsvangirai said.
"While it may not be possible to undo what has been done, it is sometimes possible to assist the victims to move on and to rebuild a life that has been shattered," he added.
Tsvangirai avoided blaming anyone for the violence, which mainly targeted his supporters.
Despite the unity government, Mugabe has proved reluctant to accept major political reforms and maintained control over security forces.