An intravascular sensor delivery device for measuring a physiological parameter of a patient, such as blood pressure, within a vascular structure or passage. In some embodiments, the device can be used to measure the pressure gradient across a stenotic lesion or heart valve. For example, such a device may be used to measure fractional flow reserve (FFR) across a stenotic lesion in order to assess the severity of the lesion. The sensor delivery device has a distal sleeve configured to pass or slide over a standard medical guidewire. Some distance back from the sensor and distal sleeve, the device separates from the guidewire to permit independent control of the sensor delivery device and the guidewire. The sensor delivery device can be sized to pass over different sizes of guidewires to enable usage in coronary and peripheral arteries, for example. The sensing mechanism (sensor) can be a fiber optic pressure sensor, such as a MEMS-based Fabry-Perot fiber optic pressure sensor, for example, or could employ some other technology, e.g., MEMS capacitive or piezoresistive sensor.