In addition to his teaching duties, Professor Shannon serves as the University's NCAA Faculty Athletics Representative. In that role, Shannon is also the Big 12 representative on the national board for the 1A FAR association where he also served three, two-year terms as President of the organization from 2012-2018. Shannon also served on the NCAA Division I governing Council from 2015-2019, and he is a past Chair of the NCAA Division I Legislative Committee.

Shannon was first appointed to the Texas Judicial Commission on Mental Health in 2018, and he is also a board appointee for StarCare Specialty Health System (formerly known as Lubbock Regional Mental Health & Mental Retardation Center), where he has served for over thirty years and twice served as chair. Shannon is an elected member of the American Law Institute and was the 2008–09 President of the Lubbock Area Bar Association. In past years, he also served on the boards of Advocacy, Inc. (now Disability Rights Texas), the Lubbock Area Bar Association, NAMI-Texas, and the Texas Council of Community Centers. He is also a past chair of the State Bar of Texas Disability Issues Committee and a former Council member of the State Bar ADR Section. Former Governor Rick Perry appointed him to four terms on the Texas Governor's Committee on People with Disabilities from 2003-11. In 2000, Shannon filed an amicus curiae brief at the United States Supreme Court in PGA Tour, Inc. v. Casey Martin. He also served through appointment by the Lt. Governor on a task force in 2002-03 that re-wrote the state's criminal competency statutes.

Professor Shannon is the author or co-author of seven editions of the book, Texas Criminal Procedure and the Offender with Mental Illness. Shannon also co-authored two editions of Rau, Sherman, & Shannon's Texas ADR & Arbitration Statutes & Commentary.

After serving as the Charles “Tex” Thornton Professor of Law for 15 years, in March 2015 the Texas Tech Board of Regents designated Professor Shannon as a Paul Whitfield Horn Distinguished Professor, the highest recognition for faculty at the University. Shannon’s University recognitions include the Texas Tech President’s Excellence in Teaching Award (twice), the Barnie Rushing Distinguished Research Award, the Texas Tech Chancellor's Council Distinguished Teaching Award, the Texas Tech Faculty Distinguished Leadership Award, and the President's Academic Achievement Award, as well as a number of teaching awards bestowed by his students. In 2020 he received the Governor's Trophy from the Governor's Committee on People with Disabilities within the Office of the Texas Governor for his “significant contributions to disability rights across the broad spectrum of disability … [and] for his work at the intersection of mental health and the legal system.”  In 2004 Shannon was awarded the Justice Frank Evans Award by the State Bar's ADR Section and was named the outstanding alumnus of Angelo State University. He has won the Outstanding Law Review Article Award from the Texas Bar Foundation three different times (2002, 2008, and 2014); the Texas Council of Community Centers selected Shannon for the Frank M Adams/Gladdie Fowler Board Service Award for outstanding volunteer service in 2021, and in 2001 he received the Mary Holdsworth Butt Award from the Texas Department of Mental Health & Mental Retardation for outstanding volunteer service.  

Shannon graduated first in his law school class. Before coming to Texas Tech, Shannon served as an attorney-advisor in the Office of the General Counsel to the Secretary of the Air Force at the Pentagon and practiced at the Austin office of Hughes & Luce (now part of K&L Gates).