Microfluidic applications demand accurate control and measurement of small fluid flows and volumes, and the majority of approaches found in the literature involve materials and fabrication methods not suitable for a monolithic integration of different microcomponents needed to make a complex Lab-on-a-Chip (LoC) system. The present work leads to a design and manufacturing approach for problem-free monolithic integration of components on thermoplastics, allowing the production of excellent quality devices either as stand-alone components or combined in a complex structures. In particular, a polymeric liquid flow controlling system (LFCS) at microscale is presented, which is composed of a pneumatic microvalve and an on-chip microflow sensor. It enables flow regulation between 30 and 230 μl/min with excellent reproducibility and accuracy (error lower than 5%). The device is made of a single Cyclic Olefin Polymer (COP) piece, where the channels and cavities are hot-embossed, sealed with a single COP membrane by solvent bonding and metalized, after sealing, to render a fully functional microfluidic control system that features on-chip flow sensing. In contrast with commercially available flow control systems, the device can be used for high-quality flow modulation in disposable LoC devices, since the microfluidic chip is low cost and replaceable from the external electronic and pneumatic actuators box. Functionality of the LFCS is tested by connecting it to a microfluidic droplet generator, rendering highly stable flow rates and allowing generation of monodisperse droplets over a wide range of flow rates. The results indicate the successful performance of the LFCS with significant improvements over existing LFCS devices, facing the possibility of using the system for biological applications such as generating distinct perfusion modes in cell culture, novel digital microfluidics. Moreover, the integration capabilities and the reproducible fabrication method enable straightforward transition from prototype to product in a way that is lean, cost-effective and with reduced risk.