In vertebrates, sexual reproduction depends on the precisely temporally controlled translation of mRNAs stockpiled in the oocyte. The RNA-binding proteins Zar1 and Zar2 have been implicated in translational control in oocytes of several vertebrate species, but how they act mechanistically is still incompletely understood. Here, we investigate the function of Zar1l, a so far uncharacterized member of the Zar protein family, in Xenopus laevis oocytes. By combining biochemical assays and mass spectrometry, we reveal that Zar1l is a constituent of a known large ribonucleoparticle containing the translation repressor 4E-T and the central polyadenylation regulator CPEB1. Employing TRIM-Away, we show that depletion of Zar1l from prophase-I arrested oocytes results in premature meiotic maturation upon hormone treatment. We provide evidence that this is based on the precocious expression of the kinase cMos, a key promotor of meiotic resumption. Based on our data, we propose a model according to which degradation of Zar1l results in dissociation of 4E-T from CPEB1, thus weakening translation inhibition imposed by the mRNA 3’UTR of cMos and probably also other M-phase promoting regulators. Thus, our detailed characterization of the function of Zar1l reveals novel mechanistic insights into the regulation of maternal mRNA translation during vertebrate meiosis.