[en] The low-lying electronic states of ThF⁺, a possible candidate in the search for $\mathcal{P}$- and $\mathcal{T}$-violation, have been studied using high-level correlated relativistic ab initio multi-reference coupled-cluster and configuration interaction approaches. For the ${}^3\mathrm{\Delta <!--\; ??\; -->}$ state component with Ω = 1 (electron electric dipole moment ‘science state’) we obtain an effective electric field of $E_{\mathrm{e}\mathrm{f}\mathrm{f}}=35.2$ $\mathrm{G}\mathrm{V}\mathrm{c}{\mathrm{m}}^{-<!--\; ???\; -->1}$, a $\mathcal{P}$- and $\mathcal{T}$-odd electron–nucleon interaction constant of $W_{P,T}=48.4$ kHz, a magnetic hyperfine interaction constant of $A_{\parallel <!--\; ???\; -->}=1833$ MHz for ²²⁹Th ($I=5/2$), and a very large molecular dipole moment of 4.03 D. The Ω = 1 state is found to be more than 300 cm⁻¹ lower in energy than $\mathrm{\Omega <!--\; ??\; -->}=0^{+}$ (${}^1{\mathrm{\Sigma <!--\; ??\; -->}}^{+}$), challenging the state assignment from an earlier theoretical study on this species (Barker et al 2012 J. Chem. Phys. 136 104305). (paper)