A Tm(III) ion-selective membrane sensor was fabricated from polyvinyl chloride (PVC) matrix membrane containing N,N’-bis(pyridine-2-carboxamido)-2-aminobenzylamine (BPCA) as a neutral carrier, sodium tetraphenyl borate (NaTPB) as anionic excluder, and nitrobenzene (NB) as a plasticizing solvent mediator. One of the most important characteristics of any membrane sensor is its relative response for the primary ion over other ions present in solution, usually expressed in terms of potentiometric selectivity coefficient. In this work, the so-called matched potential method was used for determination of selectivity coefficients of the sensor. The sensor possesses the advantages of very good selectivity over a large number of cations, especially, for lanthanide ions (Dy3+, Tb3+, Gd3+, Er3+, Lu3+, Eu3+, Ho3+, Nd3+, Pr3+, La3+, Yb3+, Ce3+, and Sm3+). To assess its analytical applicability the proposed Tm(III) sensor was successfully applied as an indicator electrode in the titration of Tm(III) ion solutions with EDTA.