The choir vault was rebuilt following the fire of 1556. All that remains of the Gothic choir built in the second half of the 13th century is the seven-sided apse and the right-hand bay.
At the crossroads of the ogival branches of the vault, a heavy hanging key decorated with classical pilasters and enhanced with paint, is hollowed out by six arcades housing statuettes.
In the lower part of the apse, a falsely Gothic arcature, made in plaster in the 19th century, contains medallions bearing the names of the patron saints of the Counts of Tonnerre.
The slender windows are very attractive. The seven stained-glass windows, which had remained in colored glass for centuries, were replaced between 1863 and 1866 by the present-day stained-glass windows (scenes from the Old and New Testaments) by Mena, a master glassmaker from Paris, who also produced the windows for the chapelle de la Vierge in 1867. (The stained glass windows in the nave and transept were made by the Vermonet workshop, a master glassmaker in Reims, from 1884 to 1888).
The stalls come from the Abbey of Saint Michel. The altar dates from the late 18th century.