METTL1, a well-established RNA methyltransferase for the N(7)-methylguanosine (m7G) methylation modification, is responsible for human tumorigenesis. Here, we aimed to examine the activity and molecular determinants of METTL1 in colorectal cancer (CRC) development. METTL1 and ribosomal RNA processing 9 (RRP9) mRNA analysis was performed by quantitative PCR. Protein expression was detected by immunoblotting and immunohistochemistry (IHC). Cell sphere formation, invasion, and proliferation were assessed by sphere formation, transwell, and MTT assays, respectively. Cell migration was tested by transwell and wound healing assays. Subcutaneous xenografts were produced to analyze the role in vivo. The influence of METTL1 in m7G methylation and stability of RRP9 mRNA was evaluated by methylated immunoprecipitation (MeRIP) assay and Actinomycin D (Act D) treatment, respectively. METTL1 was highly expressed in CRC tumors and cell lines. METTL1 depletion suppressed CRC cell proliferation, invasiveness, migratory ability, and sphere formation potential in vitro, while increased METTL1 expression had opposite effects. METTL1 positively correlated with RRP9 expression in CRC. Mechanistically, METTL1 promoted RRP9 mRNA stability by mediating its m7G methylation, and METTL1 regulated the PI3K/AKT signaling by RRP9. Increased RRP9 expression partially reversed the suppressive effects of METTL1 depletion on CRC cell phenotypes in vitro. METTL1 depletion impeded the growth of HCT-116 subcutaneous xenografts in vivo by RRP9. Our observations identified METTL1 as a crucial protumorigenic factor to drive growth, metastasis, and stemness of CRC cells through RRP9, offering new targets for combating CRC.