Tomato (Solanum lycopersium), a globally significant vegetable crop prized for its distinctive flavor, relies on efficient sugar allocation for fruit development. Despite this, the molecular module underlying the translocation of sugars from sources to sinks within the tomato remains elusive. Sugar will eventually be exported transporters (SWEETs), a class of proteins known to mediate sugar transport, have been implicated in the process. Here, we discovered that SlSWEET12c, belonged to subfamily III, which was markedly upregulated during the development of tomato fruits. The subcellular localization of SlSWEET12c-GFP to the plasma and vacuolar membrane supported its putative role in apoplasmic sucrose transport. Complementary growth in a yeast (Saccharomyces cerevisiae) mutant strain SUSY7/ura3 confirmed SlSWEET12c with sucrose transport activity. Overexpressing and CRISPR/Cas9-mediated knockdown of SlSWEET12c in tomato plants demonstrated its role in promoting sugar accumulation in fruits. Additionally, the MYB transcription factor SlMYB1R1 was obtained by screening the cDNA library of tomato, which was highly expressed during tomato fruit development with a similar pattern to SlSWEET12c. The SlMYB1R1 could bind to the SlSWEET12c promoter and regulate its activity, thereby positively promoting sugar accumulation in tomato fruits. Collectively, our findings presented a novel role for the SlMYB1R1-SlSWEET12c module in facilitating sugar accumulation and provided a basis for future efforts to breed crops with enhanced sugar content.