We report the period, eccentricity, and mass determination for the Transiting Exoplanet Survey Satellite (TESS) single-transit event candidate TOI-222, which displayed a single 3000ppm transit in the TESS 2-min cadence data from Sector 2. We determine the orbital period via radial velocity measurements (P=33.9d), which allowed for ground-based photometric detection of two subsequent transits. Our data show that the companion to TOI-222 is a low-mass star, with a radius of 0.18_-0.10_^+0.39^R_{sun}_ and a mass of 0.23+/-0.01M_{sun}_. This discovery showcases the ability to efficiently discover long-period systems from TESS single-transit events using a combination of radial velocity monitoring coupled with high-precision ground-based photometry.