Reliability of the Attitude Determination and Control Subsystem (ADCS), particularly during emergency conditions and prior to entering precise pointing modes, is of critical importance. This issue can be addressed either through reliability analysis methods or by employing hardware components with low failure rates. In this paper, magnetic torquers are considered due to their simple structure, continuous operability in different mission modes, and lack of consumable resources. Accordingly, an integrated attitude determination and control system, incorporating both attitude determination and control processes simultaneously and utilizing only magnetic torquers in all operational modes, is proposed for a low-Earth-orbit microsatellite. Attitude determination is performed using sun sensor, magnetometer, and gyroscope measurements based on the multiplicative quaternion extended Kalman filter. Sensor noise and misalignment models are incorporated to evaluate estimation performance, while major environmental disturbance torques are considered to assess system robustness. Attitude control algorithms are designed for three main operational modes, including detumbling, sun-pointing, and nadir-pointing, and their stability is proven using Lyapunov theory. Numerical simulations are conducted to evaluate system requirements and performance. The results indicate that the detumbling process is completed in less than two orbital periods, while sun-pointing and nadir-pointing accuracies better than 22° and 5° are achieved, respectively. Comparison with representative references demonstrates that the proposed ADCS can effectively operate during emergency conditions and before transitioning to high-precision pointing modes.