This according to a state daily on Saturday.
"The critical reason for my resignation is the legal framework ... within which the Zimbabwe Human Rights Commission is expected now and in the future, to carry out its mandate," The Herald newspaper quoted Professor Reg Austin as saying in a statement.
"As a national human rights institution the commission must be independent and properly capacitated." Austin cited sections of the Zimbabwe Human Rights Commission Act and electoral laws that he said impinged on the commission's work.
The commission was appointed in 2009 as part of a raft of reforms agreed on by parties in the country's power-sharing government to guarantee fair and peaceful elections.
Austin once complained about the absence of a proper office for the commission and lack of equipment that rendered the commission ineffectual.
The rights group Zimbabwe Lawyers for Human Rights (ZLHR) said Austin's resignation indicated a serious threat to the protection of human rights.
"This resignation is an unequivocal statement of the condemnation of the current operating framework particularly the excessive powers of the executive," it said.
"Lack of effective powers and independence of the commission to investigate and take strong action where human rights violations have been brought to its attention and its inability to independently investigate and take strong action in relation to electoral-related violations."
Zimbabwe is soon expected to hold elections to choose a successor to the power-sharing government formed by veteran President Robert Mugabe and long-time rival Prime Minister Morgan Tsvangirai. Previous elections in Zimbabwe have been marred by violence and intimidation. – Sapa-AFP