Tacticity　is　a　crucial　factor　affecting　the　properties　of　synthetic　polymer　materials.　Here,　we　introduce　a　type　of　chiral　organic　Brønsted　acid　catalyst,　1,1′-bi-2-naphthol-derived　N,N′-bis(triflyl)phosphoramidimidates　(PADIs),　for　the　cationic　polymerization　of　vinyl　ethers,　which　enables　the　development　of　the　first　organocatalytic,　highly　stereoselective,　cationic　reversible　addition–fragmentation　chain-transfer　(RAFT)　polymerization　of　vinyl　ethers　with　a　trithiocarbonate　chain-transfer　agent.　This　metal-free　RAFT　process　could　afford　isotactic　poly(vinyl　ethers)　with　high　stereoselectivity,　controllable　molecular　mass,　and　narrow　dispersity　at　low　catalyst　loadings　(as　low　as　200　ppm).　Moreover,　the　trithiocarbonate　chain-end　allows　for　chain　extension　to　synthesize　diblock　copolymers　comprising　an　isotactic　poly(vinyl　ether)　block,　by　a　mechanistic　switching　from　stereoselective　cationic　RAFT　polymerization　to　visible-light-regulated　cationic　and　radical　RAFT　polymerization.　©　2021　American　Chemical　Society