Tuscan Paolini, 28, the world number 12, beat the 17-year-old Andreeva, world number 38, by 6-3 6-1.
She will play Iga Swiatek in the final Saturday after the Polish world number one beat world number three American Coco Gauff in straight sets, 6-2 6-4, in the other semi at Roland Garros.
Andreeva had stunned world number two Aryna Sabalenka of Belarus in the quarters.
Paolini, from Garfagnana near Lucca and whose mother is of Polish and Ghanaian descent, is enjoying her best ever season but has said she never hoped to get this far in Paris.
Italy will have two players in the French singles finals if world number one Jannik Sinner beats Spain’s world number three Carlos Alcaraz in their Friday semi.
ANSA