Patrick began at NIST in 2006 as an NRC-NIST postdoc. At the time, his focus was on the development of an optical frequency comb metrology system for the calibration of vacuum-wavelength. In 2008 he began to investigate highly precise measurements of the refractive index of air using a Fabry-Perot cavity-based refractometer. The work culminated in one of the most accurate measurements of the refractive index of nitrogen and argon at 633 nm, and laid the groundwork for what developed into the 2012 Innovation in Measurement Science (IMS) project entitled "Reinventing pressure, temperature, and length". Since 2012 he has been part of the team attempting to use highly accurate measurements of gas refractivity to realize the pascal. As of 2017 the project is ongoing.
Since 2015 Patrick has been a staff member of the Dimensional Metrology Group, and leader of the SI Length and Traceability project.