Nitrite is commonly found in the environment, but its overuse and potential toxicity pose serious health risks. There is a strong need to develop robust and reliable methods for detecting nitrite. Herein, a novel In2O3 solution-gated electrochemical transistor (SGET) nitrite sensor was designed and fabricated for highly sensitive detection of nitrite. Different thicknesses of In2O3 thin films were prepared by sol–gel method, which were used as the channel of transistors and optimized through evaluating the electronic and electrochemical properties. To improve the catalytic oxidation of nitrite, PtAu4 nanoparticles modified reduced graphene oxide nanocomposites (PtAu4/RGO) were fabricated on the gate of transistors through electrodeposition approach. The developed sensor exhibited exceptional sensing performance in nitrite detection, which featured with low detection limit (0.1 nM nitrite) and ultra-wide linear range from 0.1 nM to 1 mM. The developed In2O3 SGET sensor displayed excellent stability and high resistance to common interfering ions, thereby demonstrating superior anti-interference performance. Nitrite in real samples of natural lake water has been accurately measured, suggesting that the designed sensor could act as an ideal transducer platform for highly sensitive and selective nitrite detection in food and environmental fields.