John received a bachelor's degree from the University of Texas at Austin. He was born and raised in Seguin and graduated from Seguin High School. He was active in high school sports, playing football and baseball before becoming a walk-on member of the University of Texas football team.

Since his college graduation, John has been employed as a Salesman at Commercial Metals Company in Seguin.

Rep. Kuempel currently serves as Chairman of the Higher Education Committee and on the Environmental Regulation Committee where he oversees air, land, and water pollution, and the environmental regulation of industrial development and is also a member of the House Administration Committee. In 2022, he was appointed by Speaker Phelan to Co-Chair the Environmental Flows Advisory Group to study public policy implications for balancing the demands on the water resources of our state.

Since 2011, John has served on the Energy Council, a non-profit organization that helps promote a balanced national energy strategy and related environmental policies at the state level. Upon completion of the 82nd legislative session, Representative Kuempel was honored with the 2011 Legislative Champion Award given by the Foundation Appraisers Coalition of Texas for his tireless efforts in reforming Appraisal Management Companies in Texas and authoring legislation to protect appraisers and consumers in the state. Representative Kuempel has been honored each session by the Texas Association of Business and has been named a "Champion of Free Enterprise".

Like his parents, the late Edmund Kuempel and Roberta Blumberg Kuempel of Seguin, John is actively involved in his community. He is a member of the Seguin Rotary Club, the Guadalupe County 100 Club, Texas Farm Bureau and Texas and Southwestern Cattle Raisers Association.

John is an avid outdoorsman and serves as a Texas Parks & Wildlife Honorary Game Warden. He is also a life member of the National Rifle Association and the Texas State Rifle Association.

John and his wife, Michelle, are parents of 18 year-old twin boys. They are active members of Faith Lutheran Church in Seguin.

The couple supports several local charitable entities such as Guadalupe Regional Hospice, Seguin Education Foundation, Wade Busby Memorial, Tejas Literacy Club, Texas Agriculture Education and Heritage Center and County Youth Shows.