Herein, we introduce a novel redox mediator based ionic liquid for selective and sensitive detection of sulfite, which is one of the challenging areas of research in food quality control and environmental safety. A phenothiazine imidazolium ionic liquid with hexafluorophosphate counter anion (PTZ-IL) was designed and synthesized as molten salt and used as redox mediator in modified electrode preparation. PTZ-IL was immobilized onto multiwalled carbon nanotubes (MWCNT) deposited glassy carbon electrode (GCE) to fabricate PTZ-IL/MWCNT/GCE modified electrode. The electrochemical performance of PTZ-IL/MWCNT/GCE was examined using cyclic voltammetry (CV) and the fabricated sensor displayed a redox couple with anodic and cathodic peak potentials at +0.707 V and +0.594 V, attributed to phenothiazine/phenothiazine radical cation redox couple. The PTZ-IL/MWCNT/GCE showed impressive electrocatalytic activity towards the oxidation of sulfite, based on which an amperometric sensor was developed for sulfite detection. The nonenzymatic sensor thus developed has shown a wide linear range of 30–1177 μM with limit of detection of 9.3 μM and sensitivity of 282.2 μA mM− 1 cm− 2 for sulfite detection. Furthermore, the modified electrode has shown prominent stability and reproducibility. © 2018 Elsevier B.V.