Girmay, of Belgian team Intermarché, sprinted ahead of Dutchman Mathieu van der Poel, who gave a thumbs up as he crossed the line to salute the performance of the young African.
Girmay, 22, is taking part in the Giro for the first time in his career.
Professional since 2020, he has 8 victories to his name, including three for the current year alone.
At the end of March, he became the first African to win a classic (Ghent-Wevelgem).
In the general classification, the Spaniard Juan Pedro Lopez (Trek) kept the leader's pink jersey acquired the previous Tuesday on Etna.
The Italian Alessandro de Marchi, who had escaped with two companions (Davide Bais and Lawrence Naesen), led the way until the last 20 kilometers.
Australian Caleb Ewan, whose team worked to limit the breakaway lead, and Briton Mark Cavendish were left behind before the final hour.
Biniam Girmay celebrates his victory during the 10th stage of the Giro on Tuesday May 17 in Jesi, Italy Luca Bettini AFP
For his part, the Frenchman Arnaud Démare let go on the last climb, about ten kilometers from the finish, in a very lively final with many starts.
Wednesday, the 11th stage presents a rigorously flat profile from Santarcangelo di Romagna to Reggio Emilia, on an often straight course of 203 kilometers.
© 2022 AFP