On T cell activation, upregulation of gene expression produces the protein required for the differentiation and proliferation of effector cell populations. RAM, the co-factor of the RNA cap methyltransferase RNMT, is upregulated following activation. Formation of the RNA cap protects RNA during synthesis and guides RNA processing and translation. Using conditional gene deletion, we found that Ram expression stabilises RNMT protein in T cells and is required for its upregulation on activation. When the Ram gene is deleted in naïve T cells, there are major impacts on activation-induced RNA cap formation and gene expression. Activated T cell proliferation is dependent on increased ribosome production; in Ram knock-out T cells activation-induced expression of ribosomal protein genes and snoRNAs is most severely reduced. Consistent with these changes, Ram deletion resulted in reduced protein synthesis, and reduced growth and proliferation of CD4 T cells. Deletion of Ram results in a similar but milder phenotype to Rnmt deletion, supporting the role of RAM as a RNMT co-factor.