Machine learning is widely used these days to extract meaningful information out of the Zettabytes of sensors data collected daily. All applications require analyzing and understanding the data to identify trends, e.g., surveillance, exhibit some error tolerance. Approximate computing has emerged as an energy-efficient design paradigm aiming to take advantage of the intrinsic error resilience in a wide set of error-tolerant applications. Thus, inexact results could reduce power consumption, delay, area, and execution time. To increase the energy-efficiency of machine learning on FPGA, we consider approximation at the hardware level, e.g., approximate multipliers. However, errors in approximate computing heavily depend on the application, the applied inputs, and user preferences. However, dynamic partial reconfiguration has been introduced, as a key differentiating capability in recent FPGAs, to significantly reduce design area, power consumption, and reconfiguration time by adaptively changing a selective part of the FPGA design without interrupting the remaining system. Thus, integrating “Dynamic Partial Reconfiguration” (DPR) with “Approximate Computing” (AC) will significantly ameliorate the efficiency of FPGA-based design approximation. In this article, we propose hardware-efficient quality-controlled approximate accelerators, which are suitable to be implemented in FPGA-based machine learning algorithms as well as any error-resilient applications. Experimental results using three case studies of image blending, audio blending, and image filtering applications demonstrate that the proposed adaptive approximate accelerator satisfies the required quality with an accuracy of 81.82%, 80.4%, and 89.4%, respectively. On average, the partial bitstream was found to be 28.6 smaller than the full bitstream .