Background: The age of children up to 59 months is a critical period for children's growth and development and the age when optimal complementary feeding is crucial. Aim: To assess optimal complementary feeding practices and associated factors among children aged 6–23 months in rural Haramaya district, Eastern Ethiopia. Methods: A community-based cross-sectional study was conducted. Statistical Package for Social Science (SPSS) version 24 was used for the analyses. Bivariable and multivariable logistic regression analysis were conducted at p-value < 0.05 and an Adjusted Odd Ratio (AOR) with a 95% Confidence Interval (CI). Results: The percentage of mothers that practiced optimal complementary feeding practices was 53.5% (95% CI: 49.2%, 57.6%). Average monthly income of the family, $37.5 to $75 (AOR = 0.52, 95% CI: 0.28, 0.98), institutional delivery (AOR = 1.61, 95% CI: 1.06, 2.46), postnatal care follow-up (AOR = 2.53, 95% CI: 1.67, 3.82), having an awareness about IYCF (AOR = 3.05, 95% CI: 1.85, 5.02), less than 30 min foot-walking to reach health facility (AOR = 2.61,95% CI: 1.65, 4.09), separate child's feeding plate (AOR = 1.75, 95% CI: 1.16, 2.64), and attendance of Infant and Young Child Feeding demonstration (AOR = 2.02, 95% CI: 1.33, 3.07) were significantly associated with optimal complementary feeding practices. Conclusion: The magnitude of optimal complementary feeding practices was below the minimum recommended level for the growth and development of children in the study area. Lack of access to and underutilization of maternal and child healthcare services were significant risk factors for suboptimal complementary feeding practices. Maternal and child health services would be essential to mitigate suboptimal feeding practices for children aged 6–23 months.