An apparatus for pre-assembling a winding for an electric machine stator or rotor includes a plurality of hairpins with two legs having non-circular cross-section, a ring including a plurality of slots and an outer containment ring acting in containment along the perimeter of the ring. An inner cam block and an outer cam block, surrounding and radially facing the inner cam block, are arranged opposite to the exit face of the ring. The cams are adapted to be crossed, in use, by the two legs when they cross the ring at the same time; the cams open into a free circular space between the two cam blocks. A method for pre-assembling a winding set for an electric machine stator or rotor is also provided. Hairpins are inserted in sequence in the slots of the apparatus. A finished winding set positioned in the free circular space is obtained by successive rotations of the ring.