A gram-scale synthesis of terminally-branched iso-fatty acids (iso-C₁₂–C₁₉) was developed commencing with methyl undec-10-enoate (methyl undecylenate) (for iso-C₁₂–C₁₄) or the C₁₅ and C₁₆ lactones pentadecanolide (for iso-C₁₅–C₁₇) and hexadecanolide (for iso-C₁₈–C₁₉). Central to the approaches outlined is the two-step construction of the terminal isopropyl group through addition of methylmagnesium bromide to the ester/lactones and selective reduction of the resulting tertiary alcohols. Thus, the C₁₂, C₁₇ and C₁₈ iso-fatty acids were obtained in three steps from commercially-available starting materials, and the remaining C₁₃–C₁₆ and C₁₉ iso-fatty acids were prepared by homologation or recursive dehomologations of these fatty acids or through intercepting appropriate intermediates. Highlighting the synthetic potential of the iso-fatty acids and various intermediates prepared herein, we describe the synthesis of the natural products (S)-2,15-dimethylpalmitic acid, (S)-2-hydroxy-15-methylpalmitic acid, and 2-oxo-14-methylpentadecane.