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Abstract The catalytic one‐bond isomerization (transposition) of 1‐alkenes is an emerging approach toZ‐2‐alkenes. Design of more selective catalysts would benefit from a mechanistic understanding of factors controllingZselectivity. We propose here a reaction pathway forcis‐Mo(CO)₄(PCy₃)(piperidine) (3), a precatalyst that shows highZselectivity for transposition of alpha olefins (e. g., 1‐octene to 2‐octene, 18 : 1Z : Eat 74 % conversion). Computational modeling of reaction pathways and isotopic labeling suggests the isomerization takes place via an allyl (1,3‐hydride shift) pathway, where oxidative addition offac‐(CO)₃Mo(PCy₃)(η²‐alkene) is followed by hydride migration from one position (cisto allyl C³carbon) to another (cisto allyl C¹carbon) via hydride/CO exchanges. Calculated barriers for the hydride migration pathway are lower than explored alternative mechanisms (e. g., change of allyl hapticity, allyl rotation). To our knowledge, this is the first study to propose such a hydride migration in alkene isomerization.