General Solomon Mujuru, 67, had been a key part of the internal battles over who would succeed President Robert Mugabe in his ZANU-PF party.
Mujuru headed a faction of the party that wanted his wife, Joice Mujuru, to succeed Mugabe as part and state president, in opposition to another faction headed by Defence Minister Emmerson Mnangagwa.
Police are investigating the cause of the fire, but have not said they suspect foul play.
National State Security Minister Sydney Sekeramayi sobbed at the scene, saying on state television: “Unfortunately our celebrated [Mujuru] is no more, and it is difficult for us all to accept this tragic fact and the tragic circumstances of his demise.”
Mujuru had helped Mugabe consolidate power in the 1970s, and his quiet background political plays since then had earned him the name of “kingmaker.”
Mugabe, who has been in power since 1980, will have a big say on who succeeds him if and when he decides to step down.