To provide a developer and an image forming method with each of which a high-resolution, high-definition image can be stably obtained over a long time period irrespective of an environment. The present invention provides a developer including at least: toner particles each containing at least a binder resin; and a composite inorganic fine powder, the developer being characterized in that: the composite inorganic fine powder has a peak at a Bragg angle (2θ±0.20 deg) of each of 32.20 deg, 25.80 deg, and 27.50 deg in a CuKα characteristic X-ray diffraction pattern; and the half width of the X-ray diffraction peak at a Bragg angle (2θ±0.20 deg) of 32.20 deg is 0.20 to 0.30 deg.