The lability of β‐ketocarboxylic acids was exploited in domino trifluoromethylthiolation/decarboxylation reactions for the formation of α‐SCF3 ketones. The reaction mechanism was investigated through experimental and theoretical studies, which revealed the involvement of both N‐SCF3 saccharin and trifluoromethanesulfenic acid F3CSOH. A metal‐free protocol for the domino trifluoromethylthiolation/decarboxylation of β‐ketocarboxylic acids is described. The catalytic reactions take place in acetonitrile in the presence of aqueous ammonium hydroxide and N‐trifluoromethylthiosaccharin. The sequence of events and reaction mechanism were established experimentally and using density functional theory calculations. This synthetic method offers a convenient alternative to known routes for the synthesis of α‐trifluoromethylthio‐substituted ketones.