Chapin was born in Wichita, Kansas. He got his first experience in California politics in 1958 at the American Legion's Boys State summer program, where he was elected the head of the Tory Party. His counterpart, the Whig Party leader, was Stacy Keach, who went into acting as a career. Chapin graduated in 1963 from the University of Southern California, where he was a member of Sigma Chi fraternity.
When Nixon ran for California Governor in 1962, Chapin, then still at USC, was a paid Field Man (on-the-ground organizational leader for election campaigns) and worked with the volunteer organization. After the 1962 campaign he was hired by H. R. Haldeman to work at the J. Walter Thompson Company, an advertising firm, in Los Angeles.
Chapin was part of Nixon's presidential campaign from 1967 to 1968, serving as Nixon's personal aide. Time described him as "young, athletic, religious, handsome, clean-cut, bright, ambitious, and tough."
He was Special Assistant to the President (1969–71), and then Deputy Assistant (1971–73). He was the appointments secretary, responsible for scheduling presidential activities, appointments, and travel. In addition, Chapin was in charge of the White House television office. Chapin also oversaw the hiring and supervising of the presidential advance men, and headed that group in 1969 to prepare for Nixon's trip to the People's Republic of China. In 1973 Chapin was named one of the Ten Outstanding Young Men of the year by the United States Junior Chamber (Jaycees) for his work on the historic China trip. Even Chinese Premier Chou En-lai was impressed with Chapin's skill at detail work, singling him out publicly in the Beijing meetings: "You are an example of how we should utilize young men in government."
It was during this time Chapin hired Donald Segretti, his former colleague from USC, to disrupt the campaigns of Democratic presidential hopefuls during the 1972 presidential primary season through acts of political "sabotage" - known as the "dirty tricks" campaign. Chapin was asked to find a "Dick Tuck" (a legendary Democratic political saboteur) type of prankster to perform the "dirty tricks" to work under H. R. Haldeman, Nixon's Chief of Staff, and the President.
Segretti later testified before a Watergate grand jury about the activities, including Chapin's supervisory role. Chapin denied any detailed knowledge of Segretti or the activities that Segretti undertook during grand jury testimony. Segretti testified, "When Dwight hired me he made it clear he was hiring me because I was a lawyer and would know what was legal and what was not." Chapin was never indicted for any of Segretti's activities. Chapin resigned to work as an executive for United Airlines, but was drawn back into the swirl of Watergate legal proceedings.
In 1974, Chapin was found guilty of making false and or misleading statements and was remanded to the California corrections camp at Lompoc (so-called "Camp Cupcake") from August 1975 to April 1976. Despite the relatively minor repercussions he remained indignant, initially vowing to appeal "all the way to the Supreme Court" (which he did) in a very hostile political climate. It was later revealed that he was earning $1000 a week while in prison, being on the payroll of W. Clement Stone Enterprises.
After his release from prison, Chapin re-entered the private sector, working at W. Clement Stone Enterprises in Chicago. From 1977 to 1979 he published a magazine called Success Unlimited. Chapin then went to work for the International Public Relations firm of Hill & Knowlton in Chicago. Later Chapin had assignments in Geneva, Switzerland; Tokyo, Japan; and Hong Kong, where he was Managing Director, Asia, for Hill & Knowlton.
In 1986, Chapin started Chapin Enterprises. The firm provided consulting services to many prestigious companies and associations. Chapin remained involved in politics, and in 1980 worked for Ronald Reagan's election as president. In 1988 he had a position in the George H. W. Bush presidential campaign. He has maintained an active interest in politics.
He is now a business consultant and mentor/coach in East Hampton, New York.