A spokesman Bill Wiggill confirmed his death on Wednesday.
A veteran of British military campaigns in colonial-era Somalia and Malaysia, Walls commanded the army of Rhodesia, as Zimbabwe was known before independence in 1980. Mugabe retained him to help integrate the liberation war fighters.
But Mugabe later accused Walls of plotting to kill him in a botched 1980 attempt. In a documented account of their conversation, Walls said if it had been his plot, Mugabe would have died. Walls went into exile in South Africa soon afterward.