In this work, the fabrication of electrochemical fluidic fused filament fabricated devices (eF4D) was accomplished using a polyethylene terephthalate glycol (PETg) non-conductive filament for the fluidic and insulating parts and a polylactic acid/carbon black (PLA-CB) composite filament for the electrodes. For the first time, it is demonstrated that 3D conductive filaments can be chemically and/or electrochemically activated inside microchannels without affecting channel dimensions and keeping their structural integrity intact. eF4Ds were morphologically and electrochemically characterized under static and hydrodynamic conditions allowing us to explore their analytical potential in both approaches. Interestingly, the electrodes activated using a combination of chemical and electrochemical activation exhibited the best electrochemical performance in static conditions whereas under hydrodynamics the electrochemically activated electrodes (without any previous chemical pretreatment) exhibited a better performance. Indeed, electrochemically activated 3D-printed electrodes integrated into eF4Ds followed the behavior predicted by the Levich model for channel electrodes and were employed for the determination of dopamine in cell culture media with excellent analytical performance. This work paves the way for the fabrication of tailored monolithic electrochemical (micro)fluidic devices with tremendous potential for the (real-time) analysis of biological samples. •Functional fully 3D printed electrochemical microfluidic devices (EMDs).•Efficient in-channel (electro)chemical electrode activation.•Fully 3D-printed EMDs followed the Levich model for channel electrodes.•EMDs were challenged towards dopamine determination in cell culture media.