[1] Most likely born in Genoa or Porlezza, Italy, his work was inspired by famous Renaissance artists such as Michelangelo and Giacomo Barozzi da Vignola.

[1] In 1564, he was elected as Architetto del Popolo Romano (Architect of the Roman People) and under this title he completed some of his most notable commissions, both public and private.

[1][4] His architectural style, rooted in functionality, drew influence from Michelangelo's Mannerism and Giacomo Barozzi da Vignola's Classicism.

[1] He also followed through with Michelangelo's plans to (re)build the Campidoglio, or Capitoline Hill, in addition to completing his work on Sforza Chapel in the Basilica of Santa Maria Maggiore.

[1] In June 1561, Giacomo della Porta came in contact with the Confraternity of the Most Holy Crucifix and put together a set of plans for the new oratory, which included a design of the façade.

[5] This style is particularly evident in the intricacies of the lower part of the façade that includes pediments (seen in the main portal, niches, and windows), triglyphs, garlands, and candelabra.

[5] His involvement in constructing the Oratory of Santissimo Crocifisso significantly shaped his career, elevating his reputation and thus securing future commissions.

[5] Della Porta's mentor, Guidetto Guidetti, was the primary architect for the Santa Caterina de' Funari starting in 1560, spanning to 1564.

The project for the Basilica of Santa Maria Maggorie began in 1562, however, Della Porta's involvement happened near the end of the construction, roughly around 1573.

[4] Della Porta and Fontana had the merit of the technical execution of a firm that sanctioned an important stage of technological advances at the end of the sixteenth century.

[10] They made a noticeable change in the bend curvature of Michelangelo's projected design, building the dome steeper, similar to the Brunelleschi model.