Hunger and malnutrition remain enormous challenges in low-income countries. Many of the malnourished live in smallholder farm households in sub-Saharan Africa. Agricultural intervention programs increasingly aspire to help alleviate hunger and malnutrition in smallholder farm households by improving on-farm productivity and market participation at the same time. However, the impact of those programs on diets and food security is not yet well understood. To examine whether such smallholder productivity and market participation promoting programs lead to better household dietary diversity and food security, we analyze the impact of IFAD’s Smallholder Productivity Promotion Programme (S3P) implemented in Zambia from 2013 to 2019 using Inverse Probability Weighted Regression Adjustment (IPWRA). We measure dietary diversity by Food Consumption Score (FCS) and Household Dietary Diversity Score (HDDS) and food security by the Months of Adequate Household Food Provisions (MAHFP). Descriptive results illustrate that beneficiary households scored higher in FCS, HDDS, and MAHFP than non-beneficiary households. Regression results demonstrate positive impacts of the program on all three indicators by 3% or more. We show that the S3P increased households’ farm productivity and income from agricultural sales, leading to the observed higher dietary diversity and food security in beneficiary households. The overall impact of the S3P on food and nutrition security is robust and promising. We highlight the importance of including nutrition education and women’s empowerment components in such interventions for improved impact.