Research on underutilized crops in Sri Lanka is limited. This study, conducted in Uva and Eastern provinces of southeastern Sri Lanka, is aimed at identifying common underutilized crops in the dominant agricultural farms, estimating their contribution to household income and food security, and understanding key actors’ (leaders of farmers’ associations, collectors/middlemen, and traders/wholesalers) knowledge of and preference for underutilized crops. Participatory rural appraisal methods were followed and snowball sampling was used for 88 semi-structured interviews with farmers who cultivate underutilized crops on their farms. In addition, 36 key actors were interviewed to explore their knowledge of and preference for potential underutilized crops. Thirty farming plots were visited to identify the composition of underutilized crops. Three mixed cropping agricultural farms—home gardens (mean area, 0.80 ha), chena (shifting cultivation, 0.82 ha), and off-season paddy lands (1.16 ha)—were observed. We identified 37 underutilized crops of which finger millet (60% of households) was most common, followed by cowpea (50%), cassava (41%), sweet melon (36%), and cashew nut (24%). Key actors prioritized four crops, namely finger millet (Eleusine coracana [L.] Gaertn.), cashew (Anacardium occidentale L.), cowpea (Vigna unguiculata L. Walp.), and mung bean/green gram (Vigna radiata L. R.Wilczek), as high potential underutilized crops. The contribution of underutilized crops to household income and food security in Uva and Eastern province was 31% and 16%, and 61% and 43%, respectively. An integrated approach can be undertaken in order to promote and sustain underutilized crops in the region for agro-biodiversity conservation and benefiting farmers.