Magnetic cavities are sudden depressions of magnetic field strength widely observed in the space plasma environments, which are often accompanied by plasma density and pressure enhancement. To describe these cavities, self‐consistent kinetic models have been proposed as equilibrium solutions to the Vlasov‐Maxwell equations. However, observations from the Magnetospheric Multi‐Scale (MMS) constellation have shown the existence of helical magnetic cavities characterized by the presence of azimuthal magnetic field, which could not be reconstructed by the aforementioned models. Here, we take into account another invariant of motion, the canonical axial momentum, to construct the particle distributions and accordingly modify the equilibrium model. The reconstructed magnetic cavity shows excellent agreement with the MMS1 observations not only in the electromagnetic field and plasma moment profiles but also in electron pitch‐angle distributions. With the same set of parameters, the model also predicts signatures of the neighboring MMS3 spacecraft, matching its observations satisfactorily. Plain Language Summary Magnetic cavities, also referred to as magnetic holes, are ubiquitous in the space plasma environment characterized by depressed magnetic field strength and enhanced plasma pressure. These structures are usually believed to result from plasma instabilities, although recent observations and simulations have suggested their quasi‐stationary nature. Kinetic models of magnetic cavities have been also proposed, which show excellent agreement with spacecraft observations to indicate the formation of quasi‐equilibrium cavities during the turbulent evolution of space plasmas. These models, however, apply only to magnetic cavities with straight field lines, and therefore cannot describe the helical magnetic cavities recently discovered by NASA's Magnetospheric Multi‐Scale (MMS) constellation. In this paper, we propose a revised model by incorporating the canonical axial momentum as an additional invariant of particle motion into the particle distributions, to resolve the self‐consistent profiles of the electromagnetic field and particle distributions within the magnetic cavity. This revision accommodates the field‐aligned current to support the helical field lines, which shows remarkable agreement with the observations from the MMS constellation. Key Points Spacecraft observations of magnetic cavities are sometimes accompanied by azimuthal magnetic field indicating the helical structure Kinetic, equilibrium model of helical magnetic cavities is developed based on four invariants of particle motion The model reproduces the MMS observations of helical magnetic cavities in both electromagnetic field and particle distributions