Summary This paper presents the validation of a software‐defined baseband (SDB) system for satellite telemetry and telecommand (TM/TC). The baseband system was developed using the open‐source GNU Radio development kit. It runs on a personal computer connected to a commercial‐off‐the‐shelf (CoTS) RF frontend. The validation process was performed by the use of a mission‐qualified satellite emulator, a state‐of‐the‐art baseband unit, and orbiting satellites. The baseband is designed to offer multimission support. Hence, it includes a suite of modulation schemes, line codes, matched filters, and Consultative Committee for Space Data Systems (CCSDS) forward error correction codes (convolutional, Reed–Solomon, concatenated, and low‐density parity‐check [LDPC]) typically employed in TM/TC missions. The figures of merit used for the validation of the TM receiver are bit error rate (BER) and frame error rate (FER). For the TC transmitter, the validated features are modulation index, power spectrum, and the physical layer operations procedures (PLOP). Graphical Abstract We present the validation of a software‐defined baseband system for satellite ground operations. Based on low‐cost software‐defined radios, the baseband show minimal performance degradation in a laboratory environement. Infield tests shows that the baseband is capable of supporting ground operations for orbiting satellites.