Abstract Warm Jupiters are close-in giant planets with relatively large planet–star separations (i.e., 10 < a / R ⋆ < 100). Given their weak tidal interactions with their host stars, measurements of stellar obliquity may be used to probe the initial obliquity distribution and dynamical history for close-in gas giants. Using spectroscopic observations, we confirm the planetary nature of TOI-1859b and determine the stellar obliquity of TOI-1859 to be λ = 38.9 − 2.7 + 2.8 ° relative to its planetary companion using the Rossiter–McLaughlin effect. TOI-1859b is a 64 day warm Jupiter orbiting around a late F dwarf and has an orbital eccentricity of 0.57 − 0.16 + 0.12 inferred purely from transit light curves. The eccentric and misaligned orbit of TOI-1859b is likely an outcome of dynamical interactions, such as planet–planet scattering and planet–disk resonance crossing.