Morgan Tsvangirai said Mugabe wants to repair his damaged reputation after a decade of chaos that brought the country to its knees, London's Guardian newspaper reported.
Mugabe's health came under scrutiny after he had to be helped from an African summit by aides.
"Robert Mugabe has been portrayed as a demon, but he himself made a contribution to that character, and I cannot defend what he did over the last 10 years in terms of violence," Tsvangirai told the newspaper.
History will be the ultimate judge of Mugabe's character, Tsvangirai said.
The prime minister said he would seek no retribution against Mugabe, 86, or his followers, if he were to become president.
"Mugabe may be part of the problem but he is also part of the solution," Tsvangirai said.