Representative Wellenkamp was born in Kirkwood and graduated from Chaminade College Prep in 1995. He graduated from Saint Louis University in 1999, Creighton University School of Law in 2003, and George Washington Law School in 2011, with degrees in Environmental Studies, Environmental Law, and Sustainable Development Law.

Wellenkamp has worked as an environmental scientist and is currently an adjunct professor at Saint Louis University and Washington University, and is the executive director of the Mississippi River Cities & Towns Initiative - an association of 105 cities along the ten-state length of the Mississippi River.

He is related to Henry Wellenkamp, a founding store owner and key figure in the history of Washington, Missouri.

He served on the St. Charles Borromeo School Board and the Military Ascent Commission, and attends St. Elizabeth Ann Seton Parish in St. Charles. He and his wife, Alejandra, live in St. Charles and have two children, Victoria Leanne and Isabel Delores.