The leader was endorsed by all party structures at the meeting held in Masvingo, 300 kilometres southeast of the capital Harare.
The congress voiced "its support to the president and first secretary comrade Robert Mugabe as the sole candidate for the forthcoming 2018 elections," said deputy secretary Eunice Sandi Moyo.
The endorsement was met with resounding applause from thousands of supporters attending the annual conference, chanting in Shona language "tongai, tongai baba" meaning "rule, rule father".
He once joked that he would rule until he turned 100.
The absence of a clear successor has sparked infighting including verbal exchanges on social media in recent weeks between factions angling for his position.
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