The presence of the thiol/thiyl catalytic cycle in cHAT olefin hydrogenation provides a unique opportunity to circumvent this challenge through use of a chiral thiol co-catalyst, introducing stereochemistry during the alkyl radical trapping/C-H bond-forming step. We note that thiols have been used as chiral HAT catalysts to provide stereocontrol through asymmetric delivery of H• to alkyl radicals. In early studies, Roberts pioneered the use of chiral thioglycosides as HAT catalysts to provide enantioinduction in olefin hydrosilylation. Recently, the Ye group developed methods with both chiral thioglycosides and cysteine-based peptide catalysts for asymmetric olefin functionalization. In additional applications of cysteinebased peptide catalysts as chiral HAT catalysts, the Miller and Knowles groups reported enantioselective HAT in the deracemization of cyclic ureas 20 and the hydroamination of olefins. From these examples and our working understanding of cHAT, we hypothesized that a chiral thiol catalyst could be used to confer asymmetry in Fe and thiol cHAT olefin hydrogenation. Here, we demonstrate the plausibility of these ideas, starting with kinetic analysis, spectroscopy, and computations that enable better understanding of the symbiotic operation of the two cycles in Scheme 2. Using this mechanistic insight, we then show that chiral thiol catalysts can indeed lead to significant stereocontrol in olefin hydrogenation. With selectivities of up to 80:20 enantiomeric ratio (er), these studies constitute the first demonstrations of asymmetric induction in iron-catalyzed mHAT reactions and ground the pursuit of highly enantioselective catalysts with mHAT on firm mechanistic footing.