After attending Phillips Exeter Academy, Allen graduated the United States Military Academy in 1963, after which he was commissioned in the Army Corps of Engineers. Two years after graduation from West Point, he volunteered for a tour in Vietnam where he served as a Military Intelligence officer assigned to the Fifth Special Forces Group. Allen sustained injuries in an early-morning mortar attack at the Dak To Special Forces camp on June 17, 1967, that necessitated the amputation of both legs below his knees. His military service and sacrifice were recognized with receipt of a Silver Star for Gallantry in Action, the Purple Heart, and the Combat Infantryman's Badge. He was airborne-qualified.
While learning to adjust to his disability and to walk on prosthetic legs, he obtained an MBA in finance and investments from Southern Methodist University in Dallas, Texas. Allen's first post-graduate position was as an investment manager for Ross Perot. His other private sector experience has spanned oil and gas exploration, real estate marketing, and mortgage lending. He has been vice president of a bank, president of three oil service companies, and co-founder of a real estate investment company in Texas.
Allen's impassioned commitment to public service and to helping veterans began with an appointment in 1979 as the Special Assistant for Administration to Texas Governor William P. Clements, Jr. In 1981, Allen was President Ronald Reagan's selection to be Deputy Administrator for the Veterans Administration (now the Department of Veterans Affairs). However, he chose to remain in Texas where in 1982 he received the Texas Republican Party's nomination to run for State Treasurer in a race that was won by former Texas State Governor Ann Richards.
In 1989, he was nominated by President George H.W. Bush and confirmed by the U.S. Senate as Assistant Secretary for Veterans Liaison and Program Coordination at the U.S. Department of Veterans Affairs. In 1991, he received his second VA confirmation as Director of the National Cemetery System, a position in which he served until the end of the Bush Administration.
Allen's dedicated efforts to support veterans' causes at the national and state levels were recognized with his nomination by the Disabled American Veterans (DAV) organization as the Texas State candidate for the national Outstanding Disabled Veteran of the year 2000. In 1993, the Military Chaplains Association awarded him their annual National Citizenship Award.
He retired in 2005 as the Public Affairs Officer for the VA North Texas Health Care System in Dallas, Texas. His current lay ministry is involved in outreach efforts to help veterans recover emotionally and spiritually from adverse wartime experiences. Allen participates in many community and civic activities, including regularly speaking at various group events and churches. Allen has addressed many audiences nationwide as a political candidate, public official, and motivational speaker. Allen's autobiography titled "Wounded Soldier, Healing Warrior" was published in 2007 by Zenith Press.
He is a member of the American Legion, Association of the U.S. Army, Disabled American Veterans, Military Order of the World Wars, Military Order of the Purple Heart, Military Officers Association, Sons of the American Revolution, Special Forces Association, Veterans of Foreign Wars, Association of Graduates of the U.S. Military Academy, and Vietnam Veterans of America.