We report on the confirmation and follow-up characterization of two long-period transiting substellar companions on low-eccentricity orbits around TIC 4672985 and TOI-2529, whose transit events were detected by the TESS space mission. Ground-based photometric and spectroscopic follow-up from different facilities, confirmed the substellar nature of TIC 4672985 b, a massive gas giant in the transition between the super-Jupiters and brown dwarfs mass regime. From the joint analysis we derived the following orbital parameters: P = 69.0480_−0.0005^+0.0004 d, M_p = 12.74_−1.01^+1.01 M_j, R_p = 1.026_−0.067^+0.065 R_j and e = 0.018_−0.004^+0.004. In addition, the RV time series revealed a significant trend at the ~350 m s⁻¹ yr⁻¹ level, which is indicative of the presence of a massive outer companion in the system. TIC 4672985 b is a unique example of a transiting substellar companion with a mass above the deuterium-burning limit, located beyond 0.1 AU and in a nearly circular orbit. These planetary properties are difficult to reproduce from canonical planet formation and evolution models. For TOI-2529 b, we obtained the following orbital parameters: P = 64.5949_−0.0003^+0.0003 d, M_p = 2.340_−0.195^+0.197 M_j, R_p = 1.030_−0.050^+0.050 R_j and e = 0.021_−0.015^+0.024, making this object a new example of a growing population of transiting warm giant planets.