In 1975, New Hampshire Deputy Attorney General
David Souter recruited McNamara out of law school to join the Office of the Attorney General, who was then
Warren Rudman. Souter would go on to become an
Associate Justice of the Supreme Court, and Rudman a two-term
senator from New Hampshire. While in the Attorney General's Office, McNamara tried
murder cases to
juries before he was thirty years old. In 1980, based on his experience in the department, McNamara authored a treatise on New Hampshire criminal law and criminal procedure,
Criminal Practice and Procedure. This became the first book published as part of the New Hampshire Practice Series. As of 2023, McNamara's
Criminal Practice and Procedure is in its seventh edition and consists of three separate volumes. This treatise has been relied upon in New Hampshire's federal courts and its Supreme Court. In 1982, McNamara authored
Constitutional Limitations on Criminal Procedure. After four years as a prosecutor for the state of New Hampshire, McNamara spent the next 30 years in private practice with the
law firm Wiggin & Nourie in
Manchester. Early on at Wiggin & Nourie, he worked for insured defendants and handled some criminal defense matters, but his prime focus eventually became commercial litigation. As a lawyer, he was president of the
New Hampshire Bar Association for the 2006 to 2007 term, and chair of that Bar Association's Legislation Committee from 2007 to 2009. While vice-president of the Bar Association, in 2005, he served a one-year term on the New Hampshire Supreme Court's Professional Conduct Committee, part of that court's attorney discipline system. McNamara also has authored a two-volume law treatise for the New Hampshire Practice Series,
Personal Injury: Tort and Insurance Practice, which is now in its fourth edition
. == Judicial service ==