Dan "Fig" Leaf was born in Shawano, Wisconsin. He was commissioned a 2d Lt in the U.S. Air Force through the Air Force ROTC program at the University of Wisconsin-Madison in May 1974, and went on active duty beginning December 10, 1974. Lt Leaf next completed Undergraduate Pilot Training at Columbus AFB, Mississippi, in November 1975, and then attended F-4 Phantom II Combat Crew Training at George AFB, California, before serving with the 7th and 9th Tactical Fighter Squadrons at Holloman AFB, New Mexico, from November 1976 to April 1978. After completing OV-10 Branco training at Patrick AFB, Florida, Capt Leaf served as an OV-10 forward air controller with the 19th Tactical Air Support Squadron, and on the staff of the 51st Composite Group and 5th Tactical Group at Osan AB, South Korea, from August 1978 to April 1980. His next assignment was on the staff of Headquarters Pacific Air Forces at Hickam AFB, Hawaii, from April 1980 to July 1981, followed by service as an F-15 Eagle pilot with the 44th Tactical Fighter Squadron, and on the staff of the 18th Tactical Fighter Wing, at Kadena AB, Okinawa, from July 1981 to June 1985. Col Leaf next attended Army Command and General Staff College at Fort Leavenworth, Kansas, and then remained on the faculty until May 1988, when he transferred to Luke AFB, Arizona, serving with the 426th Tactical Fighter Training Squadron, as Commander of the 555th Tactical Fighter Training Squadron, and later as Commander of the 58th Operations Support Squadron from May 1988 to May 1992. His next assignment was as an Air Combat Command Research Fellow and student at the Air War College at Maxwell AFB, Alabama, from June 1992 to June 1993, and then as Deputy Commander and then Commander of the 1st Operations Group at Langley AFB, Virginia, from July 1993 to July 1995. Col Leaf served as Chief of Operations for Joint Task Force Southwest Asia in Riyadh, Saudi Arabia, from March to June 1995, and then served as Deputy Chief of Operations for U.S. Forces Korea in Yongsan, South Korea, from July 1995 to June 1997. His next assignment was as Commander of the 20th Fighter Wing at Shaw AFB, South Carolina, from July 1997 to November 1998, followed by service as Commander of the 31st Fighter Wing and 31st Air Expeditionary Wing at Aviano AB, Italy, from November 1998 to January 2000. Gen Leaf next served on the staff of Headquarters U.S. Air Force in the Pentagon from January 2000 to July 2003, and during this time he served as Director of the U.S. Central Command Air Forces Air Component Coordination Element at Camp Doha, Kuwait, from February to April 2003. His next assignment was as Vice Commander of Air Force Space Command at Peterson AFB, Colorado, from August 2003 to September 2005, followed by service as Deputy Commander of U.S. Pacific Command at Camp H.M. Smith, Hawaii, from October 2005 until his retirement from the Air Force on June 1, 2008.

His 2nd Legion of Merit Citation reads:

Brigadier General Daniel P. Leaf distinguished himself by outstanding achievement in the performance of outstanding services to the United States as Commander, 31st Air Expeditionary Wing, Aviano Air Base, Italy, from 19 February 1999 to 20 June 1999. During this period, General Leaf's outstanding achievements and his dynamic leadership and initiative during Operations NOBLE ANVIL and ALLIED FORCE were pivotal to arresting ethnic cleansing in Kosovo. He assembled, bedded down, and directed around-the-clock combat operations in the largest wing in the history of both the United States Air Force and the North Atlantic Treaty Organization. The 31st Air Expeditionary Wing, consisting of 191 aircraft and helicopters from all four United States services and five North Atlantic Treaty Organization nations, sustained combat operations for 78 straight days. Ultimately, the 31st Air Expeditionary Wing's strength swelled by over 4,000 additional personnel. In all, the wing flew over 9,000 combat sorties for over 40,000 flying hours, accounting for over 25 percent of the ALLIED FORCE effort. The superior initiative, outstanding leadership, and personal endeavor displayed by General Leaf reflect great credit upon himself and the United States Air Force.