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The effects of composition on the martensitic transformation characteristics of NiTiHf shape memory alloys are systematically explored. Transformation temperatures (TTs) demonstrate a non-monotonic dependence on Ni and Hf concentrations. For Ni > 50 at%, TTs decrease with small Hf additions, attain a minimum or are completely suppressed, depending on Ni content, followed by a significant increase with Hf content. This initial drop in TTs becomes more pronounced with higher Ni contents and is attributed to the increase in nickel anti-site defects along with bulky substitutional Hf contributing to the increase in local lattice distortions along with the re-distribution of Ti and Hf.