Ti3C2Tx (MXene), a two-dimensional material prepared by solution etching, has abundant functional groups on its surface, which makes it have a great prospect in the field of biosensing environmental detection. In this work, a new optical fiber sensor integrated with MXene is proposed and fabricated. The sensor is constituted of a three-core fiber (TCF), a single-mode fiber (SMF), and a no-core fiber (NCF) to form a Michelson interference structure. The results indicate that MXene decorated fiber-optic sensor can detect trace lead ions (Pb2+) and has a good response to the Pb2+ solutions with the concentration of 0-100 μM. At 0.001 μM (i.e., 0.286 ppb) Pb2+, the response time is about 2 minutes. In addition, the fiber-optic sensor has excellent temperature, pH, and time stability. The present work provides a new idea for the detection of Pb2+ in heavy metal pollution fields.