Dionne's appointment as prime minister was confirmed Sunday by a presidential decree, Al Jazeera reported.
Dionne, 54, has worked for the UN Industrial Development Organisation, which promotes sustainable industrial growth in developing countries and economies in transition.
Since March, Dionne served as Sall's advisor.
Former prime minister Aminata Toure was sacked Friday after her party's failure to win a seat from Dakar in last week's local elections.
Toure took charge Sep 1, 2013, and was the second female prime minister of Senegal.