The development of cost-effective, robust, and rugged biochemical sensing devices is of great interest for point-of-care testing and on-spot monitoring. Here we reported a facile approach to build high-performance flexible potentiometric sensing devices by using free-standing graphene paper (GNP) as electrode substrate. The transduction mechanism of the GNP-based electrode was investigated systematically, revealing that GNP acts as both electric conductor and ion-to-electron transducer of the potentiometric signals. Three GNP-based ion-selective electrodes (GNP-ISEs) were constructed, which exhibited excellent potentiometric performance. Furthermore, a paper-type reference electrode (RE) was presented for the first time in which the photo-polymerised reference membrane is directly coated onto the GNP. Results show that the GNP-based RE (GNP-RE) displayed low potential variability for a wide range of biochemical species in a wide calibration range. On the basis of these excellent results, integrated potentiometric sensing devices using GNP-ISE and GNP-RE were built that possess comparable performance with common types of potentiometric detection system. High-performance, easy fabrication, low cost, and excellent flexibility make the GNP-based potentiometric sensing devices very attractive as 'vanguard analytical tools' for routine sensing applications.