Background: Electrifying last-mile delivery vehicles is central to cleaner urban logistics, yet behavioral evidence on commercial operators remains limited. This study examined the determinants of adoption intention among Thai delivery operators considering electric light commercial vehicles (eLCVs) or electric motorcycles (EMs) and whether these determinants are equivalent across groups. Methods: An extended Theory of Planned Behavior with perceived economic, social, and environmental benefits was tested on survey data from 729 operators using multigroup structural equation modeling with sequential invariance testing. Results: All six determinants positively and significantly affected intention in both groups. Attitude had the largest effect, followed by perceived social benefits, whereas perceived economic benefits were among the weakest. Configural, metric, scalar, and structural invariance were supported. Conclusions: The same determinants operate equivalently across both vehicle types, and adoption intention rests on evaluative and social judgments as well as cost savings. Policies and marketing can rely on common behavioral levers while tailoring delivery to each group’s operating context.