John M. Rector was born in Seattle, Washington in 1943 and was raised in Sacramento and Bakersfield, California. He graduated with honors from Garces Memorial High School in 1961 and from the University of California at Berkeley in 1966 with a degree in criminology. He earned his J.D. degree from the University of California's Hastings College of Law, serving on the editorial board of the Law Journal. In 1968 he was selected for the U.S. Department of Justice Honors Program, where he served first in the Civil Rights Division as a trial attorney and investigator assigned to criminal cases, including the "Algiers Motel" case and the killings at the Jackson State College campus, and later as a legislative specialist in the Office of Legislation.

In early 1971 Rector joined the staff of the Senate Judiciary Committee's Subcommittee to Investigate Juvenile Delinquency as deputy chief counsel. In 1973 he was appointed by the chairman, Senator Birch Bayh, to the position of staff director and chief counsel, working on drug abuse, firearms, and juvenile justice legislation and oversight. He was responsible for initiatives investigating the networks supporting availability and use of illegal drugs and for driving forward legislation establishing a separate juvenile justice system.

In 1977 Rector was confirmed by the Senate to head the Law Enforcement Assistance Administration's Office of Juvenile Justice, tasked with implementing the 1973 Juvenile Justice and Delinquency Prevention Act in the context of a constant battle for funding. Following his departure from that office in 1979 he served as special counsel to Attorney General Benjamin Civiletti.

In 1980 Rector became Director of Government Affairs for the National Association of Retail Druggists, then served as Senior Vice President for Government Affairs and General Counsel of the renamed National Community Pharmacists Association from 1986 through 2005. In 2006 he was named Senior Vice President and General Counsel, then in 2009 Senior Vice President and Special Counsel. Since 2010 he has served as advisor to the Association of Community Pharmacists Congressional Network.