This paper presents the reasoning for and the design process of contouring a high lift front-loaded low pressure turbine (LPT) airfoil near the endwall to reduce the endwall loss. The test airfoil, L2F, was designed to the approximate gas angles with 38% larger pitchwise spacing than the widely studied Pack B airfoil. Being more front-loaded with a higher stagger angle, L2F is shown to produce more endwall losses than Pack B. It is suggested that the high endwall loss of L2F is due to the high stagger angle, not front-loading, as usually suggested in the literature. A procedure is presented to approximate the front-loading and stall resistance of L2F and obtain a low stagger version of that airfoil, designated as L2F-LS. A contoured airfoil is then designed by transitioning L2F into L2F-LS at the endwall to obtain a benefit from the reduced stagger angle at the endwall. Due to the contouring process generating a fillet, the contoured airfoil is referred to as L2F-EF (“endwall fillet”). Predictions in this paper suggest endwall loss reductions between 17% and 24% at Re = 100,000. Linear cascade experiments in Part II of this paper indicate that L2F-EF reduces endwall losses more than 20% compared to L2F. The overall conclusion is that the stagger angle has a significant effect on endwall loss and should be considered for designing high lift LPT airfoils at the endwall.