The ability to generate stable transgenic mammalian cell lines is crucial to the investigation of gene functions and the production of recombinant proteins. Mammalian cells can be readily transfected in cell culture settings via both viral and nonviral vectors to induce transgene expression. However, there is an unmet need for efficient selection of transfected cells, since current methods involve rather inefficient antibiotic selection protocols or require the coexpression of fluorescent marker proteins, followed by laborious cell-sorting procedures. Thus, our aim was to implement a rapid and efficient selection approach for transgene-expressing human cells, using an engineered diphtheria toxin (DT) resistance-based selection, referred to as selecDT. We demonstrated that selecDT is expressed on the cell surface, provides efficient protection from DT by inactivating its uptake receptor, and, therefore, enables selection. SelecDT allows for greater selection efficiency in a more rapid timeline compared with conventional antibiotic methods. Thus, the resistance described herein may positively impact biotechnological processes.