This study demonstrates a new transformation path from lignin to graphene and nanodiamonds (NDs) by femtosecond laser writing in air at ambient temperature and pressure. Graphene nanoribbon rolls were generated at lower laser power. When the laser power was high, NDs could be obtained apart from graphene and onion-like carbon intermediates. These structures were confirmed by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The effects of laser power and laser writing speed on the structure of laser-induced patterns were investigated. The results show that the laser power was more important than the writing speed for the synthesis of carbon nanoparticles, and high laser power contributed to enhanced electrically conductive performance. Therefore, the direct laser irradiation technique leads a simple, low-cost, and sustainable way to synthesize graphene and NDs and is promising for the fabrication of sensors and electric devices.