The bioactivity of vancomycin is enabled by three aromatic crosslinks, the biosynthesis of which has been an active area of investigation for two decades. Two cytochrome P450 enzymes, OxyB and OxyA, have been shown to introduce bisaryl ether linkages with the help of a so-called X-domain. The final crosslink, however, a biaryl bond thought to be installed by OxyC, has remained elusive. We report the in vitro reconstitution of the OxyC reaction and formation of the first carbon-carbon crosslink in any glycopeptide antibiotic. Using a cascade sequence, in which the peptide substrate was incubated with the Oxy enzymes in turn, we completed the chemoenzymatic synthesis of a vancomycin aglycone variant. This approach was also used to generate a new analogue carrying a thioamide linkage at residue 4, a precursor to the amidine derivative, which is effective against vancomycin-resistant pathogens. Our results set the stage for creating therapeutic vancomycin derivatives by using the native metalloenzymes.