Four maleated soybean oil (SBO) derivatives were synthesized and used as bio-based reactive diluents (RDs) for alkyd coating systems. The RDs were prepared in a two-step fashion: (a) Maleation of SBO with maleic anhydride (MA) via an ene reaction followed by (b) a nucleophilic acyl substitution of the grafted succinic anhydride with allyl- or methacrylate-functional molecules. The structures were characterized using 1H NMR, 13C NMR, 13C-1H heteronuclear single quantum coherence NMR, 13C-1H heteronuclear multiple bond correlation NMR spectroscopy, FT-IR (ATR) spectroscopy, and MALDI-ToF-MS. The 2D NMR spectroscopy techniques helped confirm that MA was successfully grafted onto SBO. FT-IR spectroscopy identified new absorption bands at 1780 and 1850 cm−1, following the maleation reaction, corresponding to the anhydride functionality. Alkyd coating formulations were prepared with either 0, 10, 20, or 30 wt% of the different RDs. Brookfield viscosity measurements were conducted on the formulations to measure the efficiency of the SBO-based RDs. At 20 wt% loading level, the RDs typically reduced the viscosity of the base alkyd resin by 50%–60%. Coatings tests and gel content measurements were also conducted in order to understand the effects that these RDs had on the performance of the alkyd coatings.