Elected to the Legislative Assembly, he defended Catholic colleges, the ecclesiastical costume, and Christian marriage against the majority.
Under the Concordat of 1802, Le Coz was one of the Constitutional bishops whom the force of circumstances compelled the Holy See to recognize, and he became Archbishop of Besançon.
Bernier, the ecclesiastical diplomat who negotiated the rehabilitation of the jurors, thought it best, in order to avoid delay, not to make a clear mention of the manner of retractation required by Pope Pius VII; as a consequence, Le Coz denied ever having retracted, and the awkwardness of the situation was ended only by a personal interview between Le Coz and Pius VII, in which both were seen weeping but of which neither ever spoke.
As schismatic Bishop of Ille-et-Vilaine, Le Coz failed in his endeavour to organize the new province of which he was the metropolitan; otherwise he proved a zealous administrator and a charitable pastor.
The strange mixture in Le Coz's life, is partly explained by his intensely Gallican education, which caused him to adopt and to maintain with obstinacy schismatic views.