We propose a general analytic method to study the localization transition in one-dimensional quasicrystals with parity-time ($\mathcal{PT}$) symmetry, described by complex quasiperiodic mosaic lattice models. By applying Avila's global theory of Schr\"odinger operators, we obtain exact mobility edges and prove that edge is identical boundary $\mathcal{PT}$-symmetry breaking, which also proves e...