Small-scale tree growers (SSTGs) are critical in sustainably managing forests and rural livelihoods in Tanzania. Grounded in the Sustainable Livelihood Framework, this study characterises determinants and outcomes of livelihood diversifications among SSTGs in the Kilolo District of Tanzania. Data were collected cross-sectionally using questionnaire surveys administered to 101 households, key informant interviews (KII), and focus groups. T-test analysis reveals that socio-economic characteristics significantly influence the diversification of livelihood strategies. The Herfindahl-Hirschman Index of 0.346 indicates considerable diversification in sources of income. The multinomial logistic regression model classifies 97% of all cases, indicating an excellent fit to the data. The model analysis identifies total mean annual income, entrepreneurship, and Tree Grower Associations (TGAs) membership to be determinants of livelihood diversification among SSTGs. The study recommends that policy, institutional, market, and credit access barriers be identified and addressed to enable SSTGs to improve their highly diversified livelihood status.