This paper presents the development of a three-dimensional non-linear finite element model to predict the moment-rotational response of partial depth endplate composite connections. A parametric study is performed to evaluate the influence of utilizing various sizes (i.e., length, width, and thickness) of external Carbon Fiber Reinforced Polymer (CFRP) laminates on the composite connection performance. The numerical analysis reveals that the flexural resistance of the retrofitted CFRP strengthened composite connection increases by up to around 20% and the rotation capacity decreases by approximately 60%. Moreover, the results indicate that applying CFRP laminate to the tension face of the composite slab can reduce the amount of rebar needed for the bending capacity of steel-concrete composite beam-to-column connections.