The project of the new public building, as recalled by a plaque affixed to the façade facing the city, was entrusted to Friar Oliverio, a monk from the Abbey of Sant'Andrea in Sestri Ponente, who had previously designed the extension to the sea of the Old Pier.

The newly built palace was the seat of the Municipality for only two years; in 1262, Boccanegra was deposed and forced into exile in France, where he was appointed governor of Aigues-Mortes by Louis IX, a position he held until upon his death, in 1273 (or 1274).

From 1340 the sea palace became the seat of magistracies for the control of port traffic and the customs and the offices of the so-called "Compere" were established there, bodies responsible for managing the money loans made by citizens to the Municipality.

This was an expression of the Bank of Saint George's growing power, which brought the institution to acquire important functions not only in the economic but also political field, such as the administration of Corsica and the dominions of the republic in the two Rivieras.

The palace was restored in 1535, but the most important expansion was that of 1570, when a building was added on the eastern side, adjacent to the existing one, with a monumental façade facing the port, designed to be clearly visible to those who approached Genoa by sea.

The Lombard painter, commissioned by D'Andrade, carried out the reconstruction on the basis of what remained visible, the sketches by Tavarone and the large canvas by Paggi, preserved in the library of the palace, which depicted the façade.

At the request of the CAP, the entrance portal on the sea side was opened and a staircase leading to the Sala delle Compere was built internally by the architect Marco Aurelio Crotta.

For the opening of the staircase, the ancient "sacristies" of the Banco were sacrificed, but above all the orientation of the building was reversed which with this innovation was, for the first time in its history, related to the port rather than with the city.

The palace today presents itself in a dual aspect: towards the Ripa portico the thirteenth-century building, in exposed red bricks and stone base, and the sixteenth-century wing extending towards the port, with painted plaster.

The 16th-century wing overlooks Via della Mercanzia, with the façade entirely covered with frescoes by Raimondo Sirotti which reflect those created at the beginning of the 20th century by Ludovico Pogliaghi, who in turn had redone and reinterpreted the originals by Tavarone.

On the sides, from left to right, six bronze-coloured statues are painted inside fake niches, depicting some historical figures of the Republic: the annalist Caffaro, the "Prince" Andrea Doria, the doge Simone Boccanegra (according to some the painting instead depicts the founder of the palace, Guglielmo Boccanegra), the crusader leader Guglielmo Embriaco known as "Maulhead", the navigator Christopher Columbus and finally the admiral Benedetto I Zaccaria.

The decoration is completed by the figures of Janus and Neptune, also in fake bronze, and the coat of arms of the "Conservatori del Mare", the body responsible for governing the port at the time of the Republic of Genoa.

In the eastern part of the 16th-century wing, on Piazza Raibetta, there is a large 18th-century aedicula in marble and stucco, with a statue of the Assumption with two angels in the center, surmounted by a metal canopy.