A high-strength stainless steel seamless pipe for oil country tubular goods, the high-strength stainless steel seamless pipe having a composition that comprises, in mass%, C: 0.010% or more and 0.05% or less, Si: 1.0% or less, Mn: 0.1 to 0.5%, P: 0.05% or less, S: less than 0.005%, Cr: more than 15.0% and 19.0% or less, Mo: more than 2.0% and less than 2.8%, Cu: 0.3 to 3.5%, Ni: 3.0% or more and less than 5.0%, W: 0.1 to 3.0%, Nb: 0.07 to 0.5%, V: 0.01 to 0.5%, Al: 0.001 to 0.1%, N: 0.010 to 0.100%, O: 0.01% or less, and B: 0.0005 to 0.0100%, and in which Nb, Ta, C, N, and Cu satisfy the following formula, optionally, in mass% one or more selected from Ti: 0.3% or less, Zr: 0.2% or less, Co: 1.0% or less, Ta: 0.1% or less, Ca: 0.0050% or less, REM: 0.01% or less, Mg: 0.01% or less, Sn: 0.2% or less, and Sb: 1.0% or less, and the balance is Fe and incidental impurities, the high-strength stainless steel seamless pipe having a microstructure that is at least 45% tempered martensite phase, 20 to 40% ferrite phase, and more than 10% and 25% or less retained austenite phase by volume determined according to the measurement method specified in the description, the high-strength stainless steel seamless pipe having a yield strength of 862 MPa or more, and being characterized in having a maximum crystal grain diameter of 500 μm or less for ferrite crystal grains when crystal grains with a crystal orientation difference of within 15° are defined as the same crystal grains, the maximum crystal grain diameter determined according to the measurement method specified in the description: 5.1 × Nb + 0.5 Ta − 10 − 2.2 / C + 1.2 N + Cu ≥ 1.0, where Nb, Ta, C, N, and Cu represent the content of each element in mass%, and the content is 0 (zero) for elements that are not contained. the high-strength stainless steel seamless pipe having a composition that comprises, in mass%, C: 0.010% or more and 0.05% or less, Si: 1.0% or less, Mn: 0.1 to 0.5%, P: 0.05% or less, S: less than 0.005%, Cr: more than 15.0% and 19.0% or less, Mo: more than 2.0% and less than 2.8%, Cu: 0.3 to 3.5%, Ni: 3.0% or more and less than 5.0%, W: 0.1 to 3.0%, Nb: 0.07 to 0.5%, V: 0.01 to 0.5%, Al: 0.001 to 0.1%, N: 0.010 to 0.100%, O: 0.01% or less, and B: 0.0005 to 0.0100%, and in which Nb, Ta, C, N, and Cu satisfy the following formula, optionally, in mass% one or more selected from Ti: 0.3% or less, Zr: 0.2% or less, Co: 1.0% or less, Ta: 0.1% or less, Ca: 0.0050% or less, REM: 0.01% or less, Mg: 0.01% or less, Sn: 0.2% or less, and Sb: 1.0% or less, and the balance is Fe and incidental impurities, the high-strength stainless steel seamless pipe having a microstructure that is at least 45% tempered martensite phase, 20 to 40% ferrite phase, and more than 10% and 25% or less retained austenite phase by volume determined according to the measurement method specified in the description, the high-strength stainless steel seamless pipe having a yield strength of 862 MPa or more, and being characterized in having a maximum crystal grain diameter of 500 μm or less for ferrite crystal grains when crystal grains with a crystal orientation difference of within 15° are defined as the same crystal grains, the maximum crystal grain diameter determined according to the measurement method specified in the description: 5.1 × Nb + 0.5 Ta − 10 − 2.2 / C + 1.2 N + Cu ≥ 1.0,