The morphology, size, and distribution of Laves phases have important influences on the mechanical properties of laser-repaired Inconel 718 (IN718) superalloy. Due to the deterioration of the substrate zone, the Laves phase in the laser cladding zone of IN718 superalloy cannot be optimized by a high-temperature solution treatment. In this study, an in situ laser heat-treatment method was proposed to regulate the morphology and size of the Laves phase in the laser cladding zone of IN718 superalloy without impacting the substrate zone. In the in situ laser heat-treatment process, a laser was used to heat previously deposited layers with optimized manufacturing parameters. A thermocouple and an infrared camera were used to analyze thermal cycles and real-time temperature fields, respectively. Microstructures and micro-segregations were observed by optical microscopy, scanning electron microscopy, and electron probe microanalysis. It was found that the in situ laser heat treatment effectively changed the morphology and size of the Laves phase, which was transformed from a continuous strip-like shape to a discrete granular shape. The effective temperature range and duration were the two main factors influencing the Laves phase during the in situ laser heat-treatment process. The effective temperature range was determined by the laser linear energy density, and the peak temperature increased with the increase of the linear energy density. In addition, the temperature amplitude could be reduced by simultaneously increasing the laser power and the scanning velocity. Finally, a flow diagram was developed based on the in situ laser heat-treatment process, and the deposition of a single-walled sample with fine and granular Laves phases was detected.