Abstract Proteolytic processing of proteins is crucial for cellular homeostasis, but also regulates signaling pathways required for effector functions and cell fate decisions. Importantly, dysregulation of proteolysis poses the risk of malignant transformation through abnormal accumulation of oncogenes. The E3 ubiquitin ligase, Fbw7, mandates proteasomal degradation of several oncogenes involved in cellular proliferation, growth, and survival. To elucidate the role of Fbw7 in B cells, we studied the function of Fbw7 in a conditional knockout mouse model. Ablation of Fbw7 during early B cell development diminished the mature recirculating B cell pool in the bone marrow and decreased the B cell population in the spleen. Further, we found a drastic reduction of the B1 cells in the peritoneal cavity. A novel acute deletion model for Fbw7 in mature B1 and B2 cells, showed similar losses of mature B cells in the bone marrow and spleen. Analysis of B cell proteomes revealed defective NF-κB signaling in the absence of Fbw7. BCR-stimulation of Fbw7-deficient B cells ex vivo showed impaired growth, poor proliferation and upregulation of apoptosis. In addition to defective NF-κB signaling, the loss of Fbw7 decreased PI3K pathway signaling, hyperstabilized the well-characterized Fbw7 substrate Myc, and induced pro-apoptotic Bim protein, which supports the role of Fbw7 in survival signaling. Ectopic expression of BCL2 in Fbw7-deficient B cells added context-specific survival signals and largely rescued the apoptotic fate of these cells. Our results indicate for the first time that Fbw7 is a critical regulator in B cells, contributing to survival signaling and controlling cell death in mature B cells.