After graduating with honors from the University of North Carolina School of Law in 1987, John began his legal career at Jenner & Block in Chicago, focusing on insurance coverage matters for policyholders. He was one of the principal attorneys involved in developing Jenner & Block's insurance recovery practice on behalf of policyholders, and became a partner at Jenner & Block in 1995. In 2000, he joined Zevnik Horton, a national policyholder firm, as a partner in its Chicago office and chair of its insurance recovery practice. In 2003, when Zevnik merged with Morgan Lewis & Bockius, he opened and became the Managing Partner of Morgan's Chicago office. In 2007, he was made co-chair of Morgan's Insurance Recovery Group. He joined Reed Smith as a partner in 2008.

John is recognized as one of the top policyholder insurance practitioners in the country by Chambers USA, The Best Lawyers in America©, Legal 500 and Who's Who Legal. He co-authored the treatise Insurance Coverage Disputes, published by Law Journal Press. He writes and lectures often on insurance coverage topics, including business interruption claims, D&O liability insurance issues, environmental insurance coverage, coverage for onshore and offshore oil and gas E&P activities, and special issues relating to Lloyd's and the London insurance market.

John is a former co-chair of the American Bar Association Litigation Section's Insurance Coverage Litigation Committee. He twice co-chaired the Committee's annual meeting, and co-chaired a bi-partisan American Bar Association task force that prepared the Manual for Complex Insurance Coverage Litigation. He is a Fellow in the American College of Coverage Counsel, a select bi-partisan group of policyholder and insurer attorneys.