KOI-1783 is a Sun-like G-type star (about 1.08 solar masses, 5,922 K, 1.14 solar radii), 866 light-years from Earth. KOI-1783.01 is a 0.22-Jupiter-mass companion, with an orbital period of 134 days, discovered in 2020 via transit. KOI-1783.02 is a 15.0-Earth-mass planet, with an orbital period of 284 days, discovered in 2020 via transit. The planet was found when it crossed the face of its star, producing periodic dips in brightness that reveal its size and orbital period to space-based photometry. Mutual gravitational tugs between the planets can slowly reshape their orbits, preserving clues to the system's assembly.