Manganese tricyanomethanide, Mn[C(CN)3]2,crystallizes in an orthorhombic lattice consisting of two interpenetrating three-dimensionalrutile-like networks. In each network, the tridentate C(CN)3−anion gives rise to superexchange interactions between the Mn2+ ions(S = 5/2) thatcan be mapped onto the ‘row model’ for partially frustrated triangular magnets. We presentheat capacity measurements that reveal a phase transition at TN = 1.18 K,indicative of magnetic ordering. From magnetic-field dependentheat capacity data a saturation field Hsat = 42 kOe isestimated. The zero-field magnetically ordered structure was solved from neutronpowder diffraction data taken between 0.04 and 1.2 K. It consists of an incommensuratespiral with a temperature independent propagation vector Q = [2Q00] = [±0.62200],where different signs relate to the two different networks. This corresponds to [±0.311 ± 0.3110]in a quasi-hexagonal representation. The ordered moment μ = 3.3μBis about two-thirds of the full Mn2+ moment. Fromthe values of TNand Q,the exchange parameters J/kB = 0.15 K andJ′/J = 0.749are estimated. The magnetic-field dependence of the intensity of the(2Q00)Bragg reflection, measured for external fields H || Q,indicates the presence of three different magnetic phases. Weassociate them with the incommensurate spiral (H < 13.5 kOe),an intermediate ‘up–up–down’ phase (13.5 kOe < H < 16 kOe)and the ‘2–1’ spin-flop-like magnetic structure (H > 16 kOe)proposed for related compounds. For increasing fields,Q continuouslyapproaches the value 1/3,corresponding to the commensurate magnetic structure of the fullyfrustrated triangular lattice. This value is reached at H* = 19 kOe.At this point, the field dependence reverses andQ adoptsa value of 0.327 at 26 kOe, the highest field applied in the experiment. Except forH*, the magneticordering is incommensurate in all three field dependent magnetic phases of Mn[C(CN)3]2.