DNMT2 and NSUN2 methylate C5 cytosines outside the anticodon loop of several tRNAs, but the inconsistent phenotypes of single Dnmt2- and Nsun2-knockout mutants obscured the biological role of this tRNA modification. Here, Tuorto et al. generated Dnmt2 and Nsun2 double-knockout mice and found that lack of both tRNA methyltransferases hampers embryonic development, cell proliferation and differentiation. These effects did not depend on altered mRNA levels but on the global loss of tRNA methylation. Interestingly, the target specificities of DNMT2 and NSUN2 were complementary, and deletion of both enzymes reduced the levels of their few common tRNA targets. This, in turn, resulted in a decreased global translation rate, suggesting a central role for tRNA methylation in the control of protein synthesis.