Both buildings were built by Louis's favourite architect Pierre de Montreuil, who adapted the architectural formulae invented at Saint Germain for use in Paris.

A single nave ends in a chevet, with almost all the wall areas filled by tall narrow glass windows, between which are large exterior buttresses.

This large number of windows is also enabled by the pierre armée technique, with metal elements built into the structure of the walls to ensure the stones' stability.

[1] In September 1548, rooms above the royal suite were refurbished for Mary, Queen of Scots and the children of Henry II of France.

It stood at the crest of a slope, which was shaped, under the direction of Étienne du Pérac[3] into three massive descending terraces and narrower subsidiary mediating terraces, which were linked by divided symmetrical stairs and ramps and extended a single axis that finished at the edge of the Seine; the design took many cues from the Villa Lante at Bagnaia.

[4] "Étienne du Pérac had spent a long time in Italy, and one manifestation of his interest in gardens of this type is his well-known view of the Villa d'Este, engraved in 1573.

Unlike the parterres that were laid out in casual relation to existing châteaux, often on difficult sites originally selected for defensive reasons,[6] these new gardens extended the central axis of a symmetrical building façade in rigorously symmetrical axial designs of patterned parterres, gravel walks, fountains and basins, and formally planted bosquets; they began the tradition that reached its apex after 1650 in the gardens of André Le Nôtre.

One of the parterre designs by Mollet at Saint-Germain-en-Laye was illustrated in Olivier de Serres' Le théâtre d'agriculture et mesnage des champs (1600), but the Château Neuf and the whole of its spectacular series of terraces can be fully seen in an engraving after Alexandre Francini, 1614.

The gardens were remade by André Le Nôtre from 1669 to 1673, and include a 2.4 kilometre long stone terrace which provides a view over the valley of the Seine and, in the distance, Paris.

King James lies buried in the nearby Church of Saint-Germain; his wife Mary of Modena remained at the château until her death in 1718.