A fuel injector assembly for an internal combustion engine includes an injector body having a control valve in fluid communication with a source of fuel. A fuel nozzle assembly is employed to disperse fuel from the assembly. A high pressure fuel passage provides fluid communication between the control valve and the fuel nozzle assembly. The high pressure fuel passage has at least one end opening through the injector body and having an inner diameter. A shape memory alloy plug seals the open end of the fuel passage. The plug has a first diameter smaller than the inner diameter when inserted into the open end and a second diameter in sealing engagement with the inner diameter upon undergoing a metallurgical phase change from martinsite to austenite such that the plug generates a seal with the fuel passage. In addition, a method of making the fuel injector assembly employing a shape memory alloy plug to seal the high pressure fuel passage is also disclosed.