A novel romaine lettuce cultivar, designated Sunbelt, is disclosed. The invention relates to the seeds of lettuce cultivar Sunbelt, to the plants of lettuce line Sunbelt and to methods for producing a lettuce plant by crossing the cultivar Sunbelt with itself or another lettuce (Lactuca sp.) line. The invention further relates to methods for producing a lettuce plant containing in its genetic material one or more transgenes and to the transgenic plants produced by that method and to methods for producing other lettuce lines derived from the cultivar Sunbelt.