Jack was a corporate attorney and retired in 2019. He has written and spoken about the founding principles of the United States and has been active in several liberty-oriented groups. As an attorney he worked for Winston & Strawn, Chicago, Illinois, from 1978 to 1986, handling a variety of corporate legal matters, with an emphasis on mergers and acquisitions, public and private financing, and international transactions. He then worked as in-house corporate counsel from 1986 to 1993 and turned to private law practice from 1993 to 2013 representing a diverse group of corporate clients while acting as part-time general counsel to several publicly and privately-held companies. In 2013, he left private law practice to work as in-house corporate counsel for one of his corporate clients until his retirement in 2019.