A scalable, diastereoselective nickel-catalyzed carboiodination reaction is reported that avoids metal-based reducing agents. Novel anti-dihydroquinolones and previously unreported tetrahydroquinolines are now readily prepared. The generation of anti-dihydroquinolones is noteworthy, as this selectivity is opposite to that of the Pd variant. Mechanistic insight into the nature of the nickel-catalyzed carboiodination reaction was derived experimentally, suggesting a catalyst-controlled cyclization and stereoretentive reductive elimination.