High-spin band structures of ²⁰⁰Tl have been studied by γ-ray spectroscopic methods using the ¹⁹⁸Pt(⁷Li ,5n)²⁰⁰Tl reaction at 45MeV of beam energy. The level scheme of ²⁰⁰Tl has been extended significantly and several new band structures have been established with the observation of 60 new transitions. The πh_9/2 ⊗ νi_13/2 oblate band has been extended beyond the particle alignment frequencies. The band structures and the other excited states have been compared with the neighboring odd-odd Tl isotopes. Total Routhian surface calculations have been performed to study the deformation and shape changes as a function of spin in this nucleus. These calculations could reproduce the particle alignment frequency and suggest that the neutron pair alignment in νi_13/2 orbital induces γ softness in ²⁰⁰Tl.