The most frequent contributing factor in Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) is the acquisition of a V₆₁₇F mutation in Janus kinase 2 (JAK2) in hematopoietic stem cells (HSCs). Recent evidence has demonstrated that to drive MPN transformation, JAK2V₆₁₇F needs to directly associate with a functional homodimeric type I cytokine receptor, suggesting that, although acquiring JAK2V₆₁₇F may promote disease, there are additional cellular components necessary for MPN development. Here we show that loss of the thrombopoietin (TPO) receptor (MPL) significantly ameliorates MPN development in JAK2V₆₁₇F⁺ transgenic mice, whereas loss of TPO only mildly affects the disease phenotype. Specifically, compared with JAK2V₆₁₇F⁺ mice, JAK2V₆₁₇F⁺Mpl^−/− mice exhibited reduced thrombocythemia, neutrophilia, splenomegaly, and neoplastic stem cell pool. The importance of MPL is highlighted as JAK2V₆₁₇FMpl^+/− mice displayed a significantly reduced MPN phenotype, indicating that Mpl level may have a substantial effect on MPN development and severity. Splenomegaly and the increased neoplastic stem cell pool were retained in JAK2V₆₁₇F⁺Tpo^−/− mice, although thrombocytosis was reduced compared with JAK2V₆₁₇F⁺ mice. These results demonstrate that Mpl expression, but not Tpo, is fundamental in the development of JAK2V₆₁₇F⁺ MPNs, highlighting an entirely novel target for therapeutic intervention.