An electrochemical fluid sensor for a downhole production tool positionable in a wellbore penetrating a subterranean is provided. The wellbore has a downhole fluid therein. The electrochemical fluid sensor includes a sensor housing positionable in the downhole tool, a sensing solution positionable in the housing (the sensing solution including a mediator reactive to target chemicals), a gas permeable membrane to fluidly isolate the downhole fluid from the sensing solution (the gas permeable membrane permitting the passage of gas to the sensing solution), and a plurality of electrodes positioned about the housing a distance from the gas permeable membrane to measure reaction by the sensing solution whereby downhole parameters may be determined.