Preval picked Michele Pierre-Louis to fill the position, which has been vacant for more than two months.
Haiti has been without a prime minister since April when riots over the rising cost of food left at least seven people dead and prompted lawmakers to force Prime Minister Jacques-Edouard Alexis to quit.
Preval's first choice, Ericq Pierre, was rejected by Haitian lawmakers, as was his second, onetime adviser Robert Manuel.
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