Brain protein I3 binding protein (BRI3BP), also known as human cervical cancer oncogene 1 binding protein 3 (HCCRBP-3), is identified as a mitochondrial and endoplasmic reticulum-associated protein. It functions through interactions with BRI3 and LETM1 domain-containing protein 1 (LETMD1/HCCR-1). Despite its established implication in cell death and tumorigenesis, BRI3BP’s role within the immune system remains unexplored. This study investigates BRI3BP’s function in the inflammatory activation of macrophages, utilizing the human monocytic leukemia cell line THP-1. BRI3BP expression was modulated through either overexpression via its expression vector or suppression by small interfering RNA. Notably, BRI3BP overexpression was observed to induce apoptotic cell death, evidenced by the release of cytochrome c from mitochondria. Further investigation into mitochondrial dynamics revealed that BRI3BP overexpression alters mitochondrial membrane potential and escalates reactive oxygen species production. Moreover, modulation of BRI3BP expression significantly impacted phagocytic activity; overexpression reduced, whereas knockdown enhanced, this activity. This regulation was mediated through the activity of Ras and subsequent ERK mitogen-activated protein kinase pathway. In conclusion, BRI3BP plays a critical role in regulating apoptosis via mitochondrial activity and phagocytosis through the Ras/ERK pathway in THP1 cells. These findings shed light on BRI3BP’s function and suggest potential avenues for developing specific macrophage activity regulators during inflammatory responses.