He previously served as acting United States deputy secretary of commerce from 2013 to 2014 and 14th director of the National Institute of Standards and Technology from 2009 and 2014.

During high school, the young Gallagher spent summers working on public health and sanitation projects in Mexico, Ecuador, and Honduras under sponsorship of Amigos de las Américas.

After graduating in 1985, he taught math and science for a year at Bishop LeBlond High School in St. Joseph, Missouri, where he also served as head coach for the cross-country track team.

His research interests have included neutron and X-ray instrumentation and studies of soft condensed matter systems such as liquids, polymers, and gels.

He also served as Under Secretary of Commerce for Standards and Technology, a new position created in the America COMPETES Reauthorization Act of 2010, signed by President Obama on January 4, 2011.