He was in the class of 1837 at the École des Beaux-Arts (School of Fine Arts), where he studied under Henri Labrouste and Eugène Viollet-le-Duc.

[1] Millet recalled that Labrouste provided his own drawings to teach his pupils, including studies of classical Italian works and his own designs, since he did not trust the École's materials and was trying to reinvent the discipline of architecture.

Viollet-le-Duc wrote a passionate tribute in Millet's defense, giving high praise for a quality of the work he had done at Troyes in the face of many difficulties.

[3] Millet was assigned the task of restoring the Château de Saint-Germain-en-Laye in 1855, and was told to remove all traces of the cells that the Ministry of War had installed when it was used as a prison between 1836 and 1855.

[5] The work progressed from the north-west angle of the château and advanced eastward around the building, restoring the lines of the donjon of Charles V of France that had been concealed by the additions of Louis XIV.

[5] On 7 July 1874 Millet was given responsibility for the diocesan buildings of Reims and for completing the Clermont-Ferrand Cathedral in place of Viollet-le-Duc, who had resigned.