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Recent work has shown evidence for the prognostic significance of tumor infiltrating B cells (B‐TIL) in high grade serous ovarian carcinoma (HGSOC), the predominant histological subtype of ovarian cancer. However, it remains unknown how the favorable prognosis associated with B‐TIL relates to the current standard treatments of primary debulking surgery (PDS) followed by chemotherapy or (neo‐)adjuvant chemotherapy (NACT) combined with interval debulking surgery. To address this, we analyzed the prognostic impact of B‐TIL in relationship to primary treatment and tumor infiltrating T cell status in a highly homogenous cohort of HGSOC patients. This analysis involved a combined approach utilizing histological data and high‐dimensional flow cytometry analysis. Our findings indicate that while HGSOC tumors pre‐treated with NACT are infiltrated with tumor‐reactive CD8+ and CD4+ TIL subsets, only B‐TIL and IgA plasma blasts confer prognostic benefit in terms of overall survival. Importantly, the prognostic value of B‐TIL and IgA plasma blasts was not restricted to patients treated with NACT, but was also evident in patients treated with PDS. Together, our data point to a critical prognostic role for B‐TIL in HGSOC patients independent of T cell status, suggesting that alternative treatment approaches focused on the activation of B cells should be explored for HGSOC. [ABSTRACT FROM AUTHOR]