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As a crucial factor of their therapeutic efficacy, the currently marketed mRNA vaccines feature uniform substitution of uridine (U) by the corresponding C-nucleoside, pseudouridine (Ψ), in 1-N-methylated form. Synthetic supply of the mRNA building block (1-N-Me-Ψ−5'-triphosphate) involves expedient access to Ψ as the principal challenge. Here, we show selective and atom-economic 1N-5C rearrangement of β-d-ribosyl on uracil to obtain Ψ from unprotected U in quantitative yield. One-pot cascade transformation of U in four enzyme-catalyzed steps, via d-ribose (Rib)-1-phosphate, Rib-5-phosphate (Rib5P) and Ψ-5'-phosphate (ΨMP), gives Ψ. Coordinated function of the coupled enzymes in the overall rearrangement necessitates specific release of phosphate from the ΨMP, but not from the intermediary ribose phosphates. Discovery of Yjjg as ΨMP-specific phosphatase enables internally controlled regeneration of phosphate as catalytic reagent. With driving force provided from the net N-C rearrangement, the optimized U reaction yields a supersaturated product solution (∼250 g/L) from which the pure Ψ crystallizes (90% recovery). Scale up to 25 g isolated product at enzyme turnovers of ∼105 mol/mol demonstrates a robust process technology, promising for Ψ production. Our study identifies a multistep rearrangement reaction, realized by cascade biocatalysis, for C-nucleoside synthesis in high efficiency. Pseudouridine (Ψ), the C-nucleoside isomer of uridine, and its 1-N-methyl derivative, are incorporated in mRNA vaccines and essential for their efficiency, but difficult to synthetically access. Here, the authors report on selective and atom-economic 1N-5C rearrangement of β-d-ribosyl on uracil to obtain Ψ from unprotected U in quantitative yield [ABSTRACT FROM AUTHOR]