Martin John Bryant was born on May 7, 1967, at Queen Alexandra Hospital in Hobart, Tasmania. He was the first child of Maurice and Carleen Bryant. The family lived in Lenah Valley, but they also spent time at their beach house in Carnarvon Bay, near the Port Arthur Historic Site. In a 2011 interview, Carleen talked about her son. She mentioned that when he was young, she often found his toys broken and described him as an "annoying" and "different" child. A psychiatrist who assessed Martin said he would struggle to hold down a job because he would irritate people too much.

At the age of 12, in 1979, Martin was hospitalized at the Royal Hobart Hospital due to an injury from a firework accident. While he was in the hospital, he was interviewed by a local TV station. People around him noticed some unusual behaviors. For example, he pulled the snorkel from another boy while diving and cut down trees on a neighbor's property. At school, Martin acted disruptively and sometimes violently. He suffered bullying from other students and was described by his teachers as distant and unemotional.

Due to his behavior, Martin was suspended from New Town Primary School in 1977. Psychological assessments at that time noted that he tortured animals. He returned to school the following year, showing improved conduct, but still teased younger children. In 1980, he was transferred to a special education unit at New Town High School. There, his academic performance and behavior got worse over the years.

When he finished school in 1983, a psychiatrist assessed him for a disability pension. The psychiatrist's report noted that Martin could not read or write, only did some gardening and watched TV, and that his parents were keeping him from more severe problems. The report suggested he might have schizophrenia and warned that his parents faced a challenging future. Martin eventually received a disability pension but also worked as a handyman and gardener. A psychologist later found that he had a borderline intellectual disability with an IQ of 66, similar to an 11-year-old.

While waiting for his trial years later, Martin was evaluated by a court-appointed psychiatrist. This psychiatrist believed Martin showed a mix of conduct disorder, attention deficit hyperactivity, and Asperger syndrome. Another psychiatrist, hired by Martin's legal team, found him to be socially and intellectually impaired but did not see signs of severe mental illness.

In April 1996, Martin Bryant committed the Port Arthur massacre in Tasmania, Australia. On April 28, he began by killing David and Noelene Martin at their bed and breakfast, Seascape. He believed that they had harmed his family. After shooting them, he took their weapons and the keys to their property.

Bryant drove to the Port Arthur Historic Site, where he entered the Broad Arrow Café. He had a large blue sports bag with him. After eating, he set up a video camera and pulled out a Colt AR-15 semi-automatic rifle. He began shooting patrons and staff, killing twelve people and wounding ten within fifteen seconds. He then moved to another area of the café and fired more shots, killing another eight people and wounding two more.

As he escaped the café, Bryant shot at people in the car park, resulting in more deaths and injuries. He then targeted a mother and her two children nearby. He killed the mother and her baby, while the older child fled. He followed the child and shot her as well.

Bryant then stole a car, killing its four occupants. He continued down the road, forcing a man into the boot of another car and killing the female driver. After returning to Seascape, he set fire to the guest house with the bodies inside, and police attempted to negotiate with him.

After hours of negotiation, communication ended due to a dead battery in the phone he was using. During the standoff, he killed his hostage. The following morning, Bryant set the guest house ablaze and tried to escape but was captured by the police after suffering burns.

He was later taken to the hospital under heavy guard. Bryant was deemed fit to stand trial and initially pleaded not guilty before changing his plea to guilty. He was sentenced to thirty-five life sentences and an additional 1,652 years without the possibility of parole. After his conviction, he spent time in solitary confinement for his safety and has remained in maximum security ever since.