This paper presents stability-improvement results of a two-area power system connected with an integrated onshore and offshore wind farm (WF) using a static synchronous compensator (STATCOM). The onshore WF of 19.8 MW is based on dynamic-slip induction generator (DSIG) while the offshore WF of 100 MW is based on doubly-fed induction generator (DFIG). The q-d axis equivalent-circuit model is derived to establish the complete system model under three-phase balanced condition. A lead-lag power-oscillation damping controller (PODC) of the STATCOM is designed by using the phase-compensation method based on modal control theory to damp low-frequency oscillations of the studied two-area power system. A systematic strategy using a frequency-domain approach based on eigenvalue analysis and a time-domain approach based on nonlinear-model simulations is performed to evaluate the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed STATCOM joined with the designed PODC is capable of improving stability of the studied two-area power system connected with the integrated onshore and offshore WF under various disturbance conditions.