The sustainable utilization of available feedstock materials for preparing valuable compounds holds great promise to revolutionize approaches in organic synthesis. In this regard, the implementation of abundant and inexpensive carbon dioxide (CO₂) as a C1 building block has recently attracted considerable attention. Among the different alternatives in CO₂ fixation, the preparation of carboxylic acids, relevant motifs in pharmaceuticals and agrochemicals, is particularly appealing, thus providing a rapid and unconventional entry to building blocks that are typically prepared via waste-producing protocols. While significant advances have been realized, the utilization of simple unsaturated hydrocarbons as coupling partners in carboxylation events is undoubtedly of utmost academic and industrial relevance, as two available feedstock materials can be combined in a catalytic fashion. This review article aims to describe the main achievements on the direct carboxylation of unsaturated hydrocarbons with CO₂ by using cheap and available Ni or Fe catalytic species.