South Africa's Supreme Court of Appeal was ruling on an appeal by king Buleyekhaya Dalindyebo against his 2009 conviction and sentencing to a 15-year jail term.
The court in Bloemfontein upheld charges of arson, kidnapping, assault and "defeating the ends of justice", but it dismissed one charge of culpable homicide.
Dalindyebo's legal team argued, in vain, that the burning of three families' homes did not amount to arson because the properties could technically be regarded as belonging to the king, the eNCA news channel reported.
The appeal court ruled Dalindyebo's "behaviour was all the more deplorable because the victims of his reign of terror were the vulnerable rural poor, who were dependent upon him," according to the News24 website.
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The ruling also accused him of "dilatory and obstructive" action for changing his lawyers 11 times, causing 34 postponements to the case.
Dalindyebo is king of the Thembu, a Xhosa ethnic group that boasted Mandela as its most prominent clan member.
The king, who has spoken about his regular use of cannabis, has often clashed publicly with President Jacob Zuma, an ethnic Zulu.
Monarchs have no official power in modern South Africa, but still command loyalty among millions of people.
They are recognised in the constitution as traditional leaders and receive government funding.
Dalindyebo, who had been allowed to go free pending the outcome of his appeal, was ordered to report to prison within 48 hours.