The success of Suñol's store gradually transformed him into one of the most prominent businessmen in the Santa Clara Valley.

[4][5] In 1835, he donated the land at the northeast corner of the Plaza del Pueblo for the reconstruction of San José Church.

[3][1] Suñol, alongside his brother-in-law Antonio María Pico (who served as Alcalde of San José at the time), oversaw the construction of the church for the next eight years until its completion and consecration in 1846.

[6] In 1842, Suñol petitioned Francisco García Diego y Moreno, the Bishop of the Californias, for proper religious vestments and relics for the church.

Beginning in 1839, Suñol became a close confident and financier of John Sutter, the founder of Sacramento and an important figure in the California Gold Rush.