Saint Nicholas is perhaps the most beautiful church in Piraeus and one of the oldest in the new city of Piraeus, as it was shaped after the Independence Revolution from the Turks in 1821 and the establishment of the new Greek state after 1930.

The church belongs to the category of cross-shaped buildings and has three domes, of which the two are low, while the central one is large and elliptical, with an island-like "lantern" at its top. The external dimensions of the church are 25.85x35.60 m, and on three sides, north, south, and west, it has three identical porticos measuring 10x3.75 m, which protrude from the main church. The porticos are flat in shape with paneling, covered by gabled roofs and pediments. The main western facade has three doors, while the two side ones have one each.

The porticos are constructed from solid marble with twelve decorated Corinthian capitals, four at each entrance. The upper part of each pediment is covered with French tiles, while internally, there are 44 intricately painted square designs in blue. At the entrance, there is an elongated pronaos with a flat ceiling, above which on the right and left there are two large areas of a single women's gallery. To the right and left of the pronaos, there are two wooden staircases from which one ascends to the women's gallery. The women's galleries are topped with domes.

The church has two bell towers on either side of the pronaos. They have two-tier bases, and at their top, each is supported by four columns, upon which the marble decoration and two small domes bearing a cross rest. In each opening between the columns, there is a double marble "window" with a small column in the middle and a cross decoration at the top.

On the eastern side of the church, the three apses of the Sanctuary stand out. They are semicircular, with the two smaller ones having one window each, while the main apse has three windows with decorative solid marble cladding on the outside and colorful stained glass on the inside. Above the two small apses, there are also large double windows, similar to those on the two external sides. At the upper part of the church, on each side, there are four identical windows with marble cladding and a cornice on columns on either side.

The church is built with stone on columns with bases ranging from 1.05 to 1.50 m thick. Aside from the porticos, which are constructed entirely of marble, the whole church and the internal columns upon which the domes rest are made of masonry. Internally, the church is supported by four independent columns, upon which the structure of the three domes rests with arches and ribbed arches, which have been built with lightweight materials from Maltese stones and special type tiles.

The entire roof features six identical gabled roofs (sloped), three small gabled roofs in front and one curved above the main apse of the Sanctuary. All are covered with French tiles. The small domes have four skylight windows, while the main dome has eight. The church has a high decorative cornice around it, as well as on the six sides of the windows.

Externally, the church has a large staircase on the north side that leads to the portico, as well as in front of it, before the large western terrace. In old times, there were shops at the base of the church, while today the underground area houses rooms and a kitchen for the social and catechetical needs of the parish. From the southern side, the entrance is at the level of the adjoining road.

The church, with its ancient Greek characteristics in the three porticos, along with the surrounding square and the opposite park of the land area of the port, which has a large underground parking space, is a unique gem of modern Piraeus.