A new multi-principal-component alloy (MPCA) filler metal, Mn35Fe5(CoNiCu)20, was designed for brazing of Ni-base superalloy 600 using thermodynamic calculations (including atomic size difference, mixing entropy, mixing enthalpy, and valence electron concentration principles) and phase diagram predictions. X-ray diffraction measurement confirmed that the MPCA has a face-centered cubic (FCC) structure. The MPCA exhibited a true yield strength of 286 MPa, compressive strength of 591 MPa and fracture strain of 106%, and melting range of 1080-1150 ˚C. The optimum brazing temperature was determined to be 1200 ˚C with a wetting angle of 13.9˚ through wetting angle tests conducted over a range of temperatures. The MPCA plate was cold rolled into foils with a thickness of 300 µm for brazing. The effect of brazing time (ranging from 15 to 120 min) on the shear strength of the brazed joint was evaluated. A maximum shear strength of 530±20 MPa was achieved with a brazing time of 90 min. With increasing brazing time, the longer interdiffusion distance facilitated a stronger metallurgical bond. However, beyond 90min, the formation of Cr-Mn rich segregations, containing a mixture of brittle Cr2Mn3 and CrMn3 intermetallic compounds, at the grain boundaries of filler foils led to a lower shear strength and brittle fracture in the joint.