By integrating coherent tracking sensor functionality into a coherent communication receiver, a dual-function receiver with coherent boresight error sensing is developed for tracking in coherent free-space optical communication systems. The sensor principles are analyzed according to optical interference theory, and the boresight error detection algorithm and small signal linear model are derived. Analysis of local-oscillator beam nutation on system performance shows that the best nutation half-angle is 0.5-1 μrad, the noise equivalent angle is less than 0.02 μrad, and the communication sensitivity degradation is 0.2-0.6 dB. This technology opens new avenues for free-space optical communication system design.