The architect who finished the choir around 1250 came from the Paris area and worked in a Rayonnant style. His shafts are very attenuated; he used star-shaped abaci in straight bays; and his window tracery designs, with piled trilobes, derive from the Sainte-Chapelle. His training handling bar tracery made him the ideal architect for the vast clerestory.

The cathedral, which combines a Romanesque nave and a High Gothic choir, is notable for its rich collection of stained glass and the spectacular bifurcating flying buttresses at its eastern end. The extant cathedral was partially rebuilt on various occasions between the late 11th century and the 15th. In 1151 Geoffrey, Count of Anjou, was buried in the cathedral. It subsequently benefited from the generosity of his son, Henry II of England, who endowed a chapel for Geoffrey, from which survives Geoffrey's famous enamelled funerary plaque (Le Mans, Musee Tessé), and provided lead for roofing. In 1217 the chapter was given royal permission to breach the Gallo-Roman wall and build a new choir. The first stone of the north transept remodelling was laid in 1403, and the work was finished around 1430. Two architects worked on it, Jean de Lescluze (fl 1420s) and Jean de Dammartin. It is dedicated to Saint Julian of Le Mans, the city's first bishop, who established Christianity in the area around the beginning of the 4th century.