The effects of stress-free and stress-assisted aging at 673 K for 4 h on the one-way and two-way shape memory effect (TWSME) in ferromagnetic Ni49Fe18Ga27Co6 (at%) single crystals were investigated. Thermal cycling in the interval of stress-induced martensitic transformation was used to induce a two-way shape memory effect. A large reversible TWSME strain of up to 4.5% was observed after stress-assisted aging, which is attributed to the selection of certain precipitate variants and the corresponding favorably oriented internal stress fields formed.