Traditional biodiesel is produced from feedstocks such as vegetable oils and animal fats by converting the triglycerides with methanol in the presence of a homogeneous catalyst to produce fatty acid methyl esters (FAMEs). However, drawbacks of this process include an undesired glycerol byproduct and post-reaction processing that result in increased production costs. In this study, unrefined corn oil and waste restaurant grease containing high free fatty acids (FFA) were used to evaluate the ability of triazabicyclodecene (TBD), a non-ionic, guanidine base, to function in a high free fatty acid environment. Reactions were carried out using both methanol and dimethyl carbonate (DMC) as methylating agents. Although increasing amounts of FFAs reduced the conversion of triglycerides (TGs), the TBD catalyst, using either methanol or DMC, adequately esterified FFAs at moderate temperatures (60 °C) but was not effective in converting triglycerides. The homogeneous catalyst work aided in elucidating the reaction chemistry. This work also studied the ability of a heterogeneous catalyst (TBD supported on a layered double hydroxide) to convert both FFAs and TGs in which 80% conversion was seen for neat canola oil and 58% conversion for unrefined oil. This study illustrates that the TBD/DMC process is an effective and commercially viable method for producing sustainable biofuels.