A design approach is presented in this paper to develop an implantable circularly polarized (CP) microstrip patch antenna (MPA) embedded in a lossy material by addressing its total quality factor (Q(T)). To achieve it, the effect of high-loss tissue on effective relative permittivity and loss tangent of MPA has been thoroughly investigated. To the authors' best knowledge, it is the first time that the exact values of Q(T) with respect to the high-loss tissue and embedded depth are studied and applied to design an implantable MPA. As the calculated Q(T) is confirmed in simulation, one can understand that an implantable MPA is actually a lossy resonator with extremely low Q(T). As such, CP radiation can be achieved by enlarging its truncated area to appropriately separate two degenerate modes in such high-loss environment. The designed implantable MPA is then exhibited to achieve a broad impedance bandwidth, wide 3 dB axial ratio bandwidth and beamwidth, and high realized gain at 2.4 GHz industrial, scientific, and medical band. After the studies of sensitivity, biocompatible materials, and model integrity are carried out, the designed implantable MPA is fabricated and tested. Simulations are accompanied by measurements with good agreement, thus underlying the importance of our approach.