A native of Shawano, Wisconsin, Leaf earned his commission as a distinguished graduate of the University of Wisconsin–Madison Air Force ROTC program in 1974.

In 1995, LtGen Leaf served as the J-3 for Joint Task Force-Southwest Asia and flew the F-15C over Southern Iraq, enforcing U.N. sanctions on the Saddam Hussein regime.

During Operation Allied Force, LtGen Leaf commanded the 31st Air Expeditionary Wing, which included F-16CG, F-16CJ, F-15E, F-117A, A-10A and EC-130 aircraft squadrons.

He flew and led F-16CG day and night combat missions against fixed and mobile targets in Serbia and Kosovo.

He worked for Northrop Grumman Information Systems as the Vice President, Strategic Initiatives, from September 2008 to January 2012.