Purpose: Selinexor is an oral selective inhibitor of exportine-1 (XPO1) with efficacy as a single agent in heavily pretreated diffuse large B-cell lymphoma (DLBCL). We conducted a study investigating the combination of selinexor with rituximab and platinum-based chemotherapy in B-cell lymphoma. Patients and methods: We conducted a phase 1b, dose-escalation, and expansion trial, which enrolled patients with relapsed or refractory B-cell non-Hodgkin lymphoma. Patients received oral selinexor according to a 3 + 3 design in combination with rituximab and dexamethasone, high-dose cytarabine, oxaliplatine (DHAOX) or gemcitabine, dexamethasone, and cisplatin (GDP) chemotherapy. Results: A total of 39 patients were enrolled, 27 during the escalation phase and 12 during the expansion phase. Most patients had diffuse large B-cell lymphoma (DLBCL; 77%). Group R-DHAOX was prematurely closed to inclusion due to a recommendation from the French drug agency, independent of this trial. A recommended phase 2 dose (RP2D) of selinexor in association with R-GPD was established at 40 mg on days 1, 8, and 15 of each 21-day cycle. In a population of 18 patients treated at this dose of selinexor, the most frequent grade 3–4 adverse events were hematological. With this regimen, seven obtained a complete metabolic response and five a partial response. The median PFS was 5.8 months. Conclusions: Among the patients with R/R B-cell lymphoma, selinexor at a weekly dose of 40 mg with R-GDP is feasible for outpatients, with a generally acceptable safety profile.