John McMahon graduated Magna Cum Laude from Seton Hall University in 1984. Upon graduation he was appointed the Director of the Essex County Prosecutor’s Victim Witness Assistance Program. John held this position, while attending Seton Hall Law School Evening Division program. He frequently advocated for his clients in court and before the State Violent Crimes compensation board. Upon graduation from Law School in 1989, John was hired as an associate at Whipple, Ross and Hirsch. He was admitted to the bar in December of 1989 and within five months was trying his first criminal case in the United States District Court for the State of New Jersey. His client was acquitted of all charges.

Seeking greater opportunities to try cases, John joined the New Jersey Office of the Public Defender.  Upon his hiring in October of 1990, he was assigned to the Essex Adult Trial Region which was then and remains the State’s busiest trial region. From 1990 to 1997 John handled all indictable matters: drug cases, thefts, burglaries, robberies, aggravated assaults, sexual assaults, kidnappings, attempted murders, murders and death penalty cases. In 1997 John was appointed Chief Trial Attorney and in that position oversaw all homicide and complex litigation. From 1997 through 2017 John continued trying murder cases and other high-profile matters.

In addition to defending his clients in over 170 jury trials, John has successfully litigated the admissibility of evidence against his clients, securing for them dismissals or favorable results without the need to go to trial. The evidential challenges that John has  mounted on behalf of his clients have included challenging the admissibility of cell tower evidence, DNA evidence, fingerprint evidence, ballistic evidence, and the use of blood alcohol extrapolation evidence in vehicular homicide prosecutions.

In addition to challenging this evidence at the trial level, John has argued before the New Jersey Appellate Division on numerous occasions and has appeared before the New Jersey Supreme Court on four prior occasions.

Simultaneous to his expansive career at the Office of the Public Defender he has been an adjunct faculty member at Rutgers Law School for over 20 years. John has taught Evidence to generations of New Jersey lawyers, many of which have gone on to become successful trial attorneys and judges.

In October of 2017, at The Public Defender’s 50th Anniversary Gala, New Jersey Public Defender Joseph Krakora named John as one of only four recipients of the Public Defender’s Lifetime Achievement Award.

After a successful career in the Office of the Public Defender, John entered into private practice in January of 2018. He looks forward to continuing to provide a strong and vigorous defense for his clients. Throughout his almost three decades of defending those accused of crimes, John understands that anyone can be accused  and when that time comes they need an advocate on their side as they fight for justice.