The title compound, [Tl(2)(C(3)H(10)NO(9)P(3))](n), a Tl(I) organic-inorganic hybrid complex, was synthesized by the reaction of nitrilo-tris(methyl-enephospho-nic acid) with thallium(I) nitrate. There are two types of Tl(+) ions in the complex, with coordination numbers of eight and seven and with stereochemically active and inactive lone-pair electrons, respectively. In the crystal, the doubly deprotonated ligands form two-dimensional hydrogen-bonded layers through O-H⋯O hydrogen bonds. The NH group is involved in a trifurcated intra-molecular hydrogen bond. Coordination of the phospho-nate ligands to the Tl(+) ions creates a three-dimensional structure.