John S. Campbell is a Maine native, having grown up in South Portland, and graduating with high honors from South Portland High School.  After graduating from Bowdoin College in 1977 with a major of Political Science and Economics, he attended the University of Maine School of Law.  During law school, he worked at the U.S. Attorney's Office under then-U.S. Attorney George Mitchell. 

Following law school he served as a law clerk for U.S. Bankruptcy Judge Frederick Johnson in Portland, Maine. He then clerked for two years for U.S. District Judge Conrad Cyr in Bangor, Maine.  After his clerkships, John began working as an associate for former U.S. Bankruptcy Judge Richard E. Poulos on Exchange Street in Portland.  His work focused on complex business litigation and commercial disputes, the highlight of which was a multi-million dollar verdict against a large financial institution for defamation and breach of contract. 

In 1993 John began a law firm on Free Street in Portland, Maine, known as Poulos, Campbell & Zendzian.  That firm was later renamed Campbell & Associates, P.A. It is located at 59 Baxter Boulevard, continuing its focus on complex business litigation as well as a variety of other practice areas.