The title complex, [MnHg(NCS)4(C2H5NO)2]n, consists of slightly distorted MnN4O2 octahedra and HgS4 tetrahedra. Each Mn(II) cation is bound to four N atoms of the NCS groups and two O atoms of the N-methylformamide (NMF) ligands in a cis configuration. Each Hg(II) cation is coordinated to four S atoms of NCS groups. Each pair of Mn(II) and Hg(II) cations is connected by an -NCS- bridge, forming an infinite three-dimensional -Mn-NCS-Hg- network.