Recently, metal-halide perovskite nanocrystals (NCs) have shown major development and have attracted substantial interest in a wide range of applications, such as light-emitting diodes (LEDs), solar cells, lasers, and photodetectors due to their attractive properties, such as superior PL emission, a wider range of color tunability, narrow emission spectra, better color purity, low cost, easy solution-processability, and so on. In the past, many color-converting materials, such as III-nitrides, organics, polymers, metal chalcogenides, were investigated for solid-state lighting (SSL) white light-emitting diodes (WLEDs). Still, they suffer from issues such as low stability, low color rendering index (CRI), high correlated color temperature (CCT), low luminous efficiency (LE), and high cost. In this sense, metal-halide perovskite NCs exhibit a better color gamut compared with conventional lighting sources, and production costs are comparatively cheaper. Such materials may offer an upcoming substitute for future color-converting WLEDs. In this review, we discuss the metal halide perovskite NCs and their synthesis protocols. Then we elaborate on the recent progress of halide perovskite NCs as a conversion layer in the application of WLEDs.