The choir is ten steps higher than the nave and surrounded by an ambulatory. There are two organs on the balconies.

One of the great Parisian churches built during the Second Empire as part of Baron Haussman's plans. The monumental appearance of La Trinité corresponds to the worldly nature of its parishioners, and its decoration is rich and theatrical, combining French and Italian Renaissance elements applied to a Gothic Revival structure. The porch tower is a sort of campanile topped by a dome and linked to the church by an open structure with a pitched roof. Exterior figures of Faith, Hope, and Charity on the church were sculpted by Eugène-Louis Lequesne.