Tuberculosis (TB), a life threatening communicable disease, is mainly caused by the bacterium named Mycobacterium tuberculosis (MTB). This high burden infectious threat is the ninth leading killer disease worldwide and also the foremost cause of death from a single infectious agent, even ranking above HIV/AIDS. In this work, a novel magnetic biosensing technique based on giant magneto-resistance (GMR) has been proposed for the on-field detection of Tuberculosis (TB) through assessment of MTB specific protein- ESAT-6. This portable highly sensitive diagnostic tool provides the results with a low turnaround time and the achieved limit of detection in the range of pg/ml can be a breakthrough in TB diagnostics. In addition, the use of DARPins (designed ankyrin repeat proteins) leads to high specificity and help in early detection, thus enabling early onset of treatment and thereby reduced mortality. This study compares the results of conventional and GNP-ELISA and it has been shown that the proposed GMR technique is more sensitive. Further, the effect of different sized magnetic nanoparticles on the performance of GMR biosensor is also presented.