Born and raised in Indiana, Keith is one of eight children of a Korean war veteran Ted Denning and his wife Phyllis Denning in a strong Catholic tradition family. Keith attended Indiana-Purdue University at Fort Wayne to earn his Nursing degree. He then went to Wake-Forest Bowman Gray Medical Center for his certification as a Certified Registered Nurse Anesthetist.

With his wife Christine, they have one son who practices law in New York City. After living in Cincinnati for 35 years, they moved to Connecticut to be closer to his son, daughter-in-law, and three grandchildren. He currently resides in Wilton, Connecticut and retired in May of 2022 after 39 years of practice.

Keith has been a volunteer on medical missions with Operation Smile and the Palestinian Children's Relief Fund and has provided free medical care all over the world. With a strong tradition of serving in all the communities where he has lived, Keith is now in his first term in Hartford. He serves on the Transportation, Public Health and Insurance and Real Estate Committees.