Victor Baltard was one of the architects preferred by Baron Haussmann, the prefect of the Seine who conducted a major campaign to modernise Paris, and his name is associated with the "huge iron umbrellas" of his covered market places. The design of the church he was commissioned to build in 1860 was conditioned by the triangular plot of land and Haussmann's desire for a dome to complete the new boulevard Malesherbes.
Starting from a narrow façade, the nave widens out towards the choir. The building is faced with stone, while the framework is entirely metal, a synthesis between iron and traditional forms partly inspired by the cathedral of Santa Maria dei Fiori in Florence. The façade has a porch with three arches, the pillars of which are surmounted by the symbols of the four evangelists, a gallery carved with the figures of Christ and the twelve Apostles, a big rose window framed by a wide pediment and a dome with a cupola rising to a height of sixty metres. The three doors on the façade were made by Christofle and the overall design mingles Romanesque and Renaissance elements. The rich ornamentation of the façade – forty-five figures carved from stone, twelve casts in bronze and three painted on lava – was emphasised by contemporary critics.
The architect Louis-Auguste Boileau was the first to use iron and cast iron in a church, in Saint Eugène, Paris, in 1853; his imaginative use of Gothic forms gave an impression of amplitude by multiplying the perspectives. Saint Augustin is perhaps less inventive but the interior is impressive. The monument stands out against a backdrop of standard apartment buildings and offers an example of successful urban scenography.