Lamy will succeed current Director-General Supachai Panitchpakdi Sept. 1. He said his "first, second and third priority" will be the completion of the Doha round of trade talks.
"I believe that we have a crucial task ahead ... to ensure that trade opening continues to contribute to development and that we place the interests of developing countries at the center of the world," Lamy said.
Panitchpaki congratulated Lamy on his appointment.
The selection process lasted five months. Lamy was chosen over three other candidates: Carlos Perez del Castillo of Uruguay, Jaya Krishna Cuttaree of Mauritius and Luiz Felipe Seixas Correa of Brazil.