Adequate nutrition during the complementary feeding period is critical for optimal child growth and development and for promoting long-term educational attainment and economic potential. To prioritize limited public health resources, there is a need for studies that rigorously assess the influence of multicomponent integrated nutrition interventions in children younger than age 2 years in different contexts. This study aimed to describe the rationale and protocol for the Saqmolo' Project using the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) guidelines. The Saqmolo' (ie, "egg" in the Mayan language, Kaqchiquel) Project is an individually randomized, partially blinded, controlled comparative effectiveness trial to evaluate the influence of adding delivery of a single whole egg per day to local standard nutrition care (ie, growth monitoring, medical care, deworming medication, multiple micronutrient powders for point-of-use food fortification [chispitas], and individualized complementary and responsive feeding education for caregivers) for 6 months, compared with the local standard nutrition care package alone, on child development, growth, and diet quality measures in rural indigenous Mayan infants aged 6 to 9 months at baseline (N = 1,200). The study is being executed in partnership with the Wuqu' Kawoq/Maya Health Alliance, a primary health care organization located in central Guatemala. Primary outcomes for this study are changes in global development scores, assessed using the Guide for Monitoring Global Development and the Caregiver Reported Child Development Instruments. Secondary outcomes include changes in infant hemoglobin, anthropometric measures (including z scores for weight for age, length for age, weight for length, and head circumference for age), and diet quality as measured using the World Health Organization's infant and young child feeding indicators. The results of the Saqmolo' Project may help to inform public health decision making regarding resource allocation for effective nutrition interventions during the complementary feeding period.