His tenure, during which the diocese was elevated to an archdiocese, was at a time of growth in the city, which he matched with the most rapid church expansion in the history of New Orleans.

On 1 July 1817 he embarked from Bordeaux with Louis William Valentine Dubourg Bishop of the Diocese of Louisiana and the Two Floridas, who had traveled to Europe to recruit clergy.

Blanc and a number of seminarians stayed with Charles Carroll of Carrollton until the end of October when they joined Dubourg in Baltimore.

Blanc proceeded to build a log chapel at a French settlement on the Illinois side of the Wabash, about twelve miles from Vincennes.

[2] Dubourg lent Blanc's services to Benedict Joseph Flaget, Bishop of the Diocese of Bardstown, whose area included most of Kentucky, Tennessee, Missouri, Illinois, Indiana, Ohio, and Michigan.

In 1827, Blanc, Armand Duplantier, Fulwar Skipwith, Thomas B. Robertson and Sébastien Hiriart received permission from the state legislature to organize a corporation called the Agricultural Society of Baton Rouge.

Blanc's institution building during the rapid growth of New Orleans and the states resulted in the number of churches increasing from 26 to 73, and of priests from 27 to 92.