A method for horizontal assembly of a high-voltage feed-through bushing includes vertically-assembling a field shaper assembly of a high-voltage feed-through bushing on a field shaper fixture. The field shaper assembly is then rotated within the field shaper fixture such that the field shaper assembly is oriented on a horizontal axis. Next, an insulator tube fixture supporting an insulator tube assembly is positioned adjacent to the field shaper fixture. The insulator tube assembly, being oriented on the same horizontal axis as the field shaper assembly, is then affixed to field shaper assembly.