We report the formation pathway of ScVO4 zircon from ScVO3 bixbyite with emphasis on the synthesis and stability of the novel intermediate defect zircon phase ScVO4-x (0.0 < x <= 0.1). The formation pathway has been investigated by means of thermogravimetric/differential thermal analysis and in situ powder X-ray diffraction. The oxidation of ScVO3 to SCVO4 involves two intermediates of composition ScVO3.5+y (0-00 <= y <= 0.22) and the novel phase ScVO4-x. ScVO4-x crystallizes in the defect zircon structure in space group /4(1)/amd (141) with a = 6.77761(5) angstrom and c = 6.14045(8) angstrom. Oxygen defect concentrations in bulk ScVO4-x samples range from 0.0 < x <= 0.1. ScVO4-x is compared with the fully oxidized zircon structure ScVO4 using powder X-ray diffraction, neutron diffraction, and bulk magnetic susceptibility data as well as Sc-45 and V-51 solid state NMR spectroscopy. ScVO4-x can only be obtained by oxidation of ScVO3 or ScVO3.5+y while the reduction of ScVO4 does not yield the novel defect structure. Mechanistic insights into the oxidative formation of ScVO4 via the defect structure are presented.