The effects of neutron heating are investigated in fast ignition laser fusion targets using deuterium–tritium (DT) fuel, ranging from ignition-scale to high-gain targets. Simulations were performed using a radiation-hydrodynamic code incorporating energetic particle transport with a particle-based scheme, in which thermal and fluid motion effects were included in both the generation and interaction processes of energetic particles. In the ignition phase, neutron heating contributes to the heating of the hot spot and its surrounding region involved in ignition, accounting for approximately 20% of the α-particle heating. This reduced the external heating energy required for ignition by approximately 10%. Additionally, neutron heating increases the fusion output in the ignition-scale fuel by about 20% at maximum, where the burn temperature remains lower than that at the peak of the DT fusion reactivity. In contrast, in high-gain fuel, neutron heating alters the burn propagation mode: α-particle-driven propagation accompanied by a compression wave changes to a faster mode in which neutrons preheat a broad region ahead of the compression wave. This induces earlier fusion reactions, causing the compression wave to be overtaken and eventually dissipate. This earlier propagation causes a reduction of more than 10% in the burn-up fraction and the fusion output due to the shortening of the burning duration. Although the effects of thermal and fluid motions have minimal impact on the ignition or burning behavior, they significantly alter the energy spectra of the escaping energetic particles, which may affect the consideration of reactor design.