The escalating demand for fossil fuels has raised environmental concerns, urging the exploration of biosynthetic pathways for renewable hydrocarbon fuels. Terminal alkenes (α-alkenes) emerge as "drop-in" compatible fuels and chemicals, holding the potential to replace traditional fossil fuels. Fatty acid decarboxylases present a promising route for converting fatty acids into α-alkenes, underscoring the imperative need for comprehending the catalytic mechanisms governing these enzymes in the quest for renewable biofuel production. The reported fatty acid decarboxylases entail the involvement of heme and non-heme iron cofactors in the redox process. In this review, we summarize the reaction mechanisms of four iron-dependent fatty acid decarboxylases (OleTJE, OleTPRN, UndA, and UndB), providing a critical analysis of the factors influencing chemical selectivity and catalytic performance.