Brenton Harrison Tarrant was born on October 27, 1990, in Grafton, New South Wales, Australia. He grew up in Grafton and attended Grafton High School. Tarrant's early life was marked by several challenges, as his parents separated when he was young. This separation, along with other traumatic events such as a house fire that led to the loss of their family home and the death of his grandfather, caused Tarrant to develop social anxiety.

After the separation, Tarrant and his sister, Lauren, lived with their mother and her new partner. This relationship became abusive, with Tarrant, his sister, and their mother facing violence from the partner. Eventually, the two children moved in with their father, Rodney Tarrant.

During his teenage years, Tarrant struggled with weight gain, leading to bullying at school. He had few friends and was often disengaged in his studies, although he displayed a strong interest in certain topics, particularly World War II. Tarrant began showing signs of racism at an early age, expressing concerns about immigration when he was just twelve. He often made derogatory comments about his mother’s former partner's Aboriginal heritage, which caught the attention of a high school teacher who intervened.

At 14, Tarrant started using the online platform 4chan. He expressed doubts about having autism and hinted at feeling sociopathic. By 2007, when he was around 16 or 17, his father was diagnosed with pleural mesothelioma, a type of cancer caused by asbestos exposure. To cope with the stress, Tarrant began working out, losing a significant amount of weight during this period.

Tarrant qualified as a personal trainer in mid-2009 after joining the Big River Gym in Grafton. In 2010, he discovered his father dead by suicide, having agreed with him beforehand that he would take this act. Tarrant inherited about A$457,000 from his father, primarily from an asbestos settlement. After suffering an injury in 2012, he left the gym and decided to travel using his inheritance.

From 2012 onward, Tarrant traveled alone to multiple countries, with one notable trip to New Zealand in March 2013. During this trip, he stayed with a friend who was a keen shooter and got his first experience with firearms at a shooting club. His travels later raised suspicions, with investigations by police in Bulgaria and Turkey regarding his connections to far-right organizations during his time in Europe.

In August 2017, Tarrant settled in Andersons Bay, Dunedin, New Zealand, where he became a member of a local gun club. He remained unemployed, using his inheritance and investment income to support his living costs. Throughout his time in Dunedin, Tarrant's mental health became a concern to his family, especially after he mentioned suicidal thoughts and stated intentions to move to Ukraine.

Tarrant's online activities included engagement with far-right ideologies, and he linked up with various groups that promoted these views. By June 2016, those close to him noted a significant change in his personality, which he claimed stemmed from a mugging incident in Ethiopia.

On 15 March 2019, Brenton Tarrant committed a mass shooting at two mosques in Christchurch, New Zealand. The first location was the Al Noor Mosque, where he attacked at 1:40 PM. Tarrant began his assault by firing a shotgun at the mosque entrance, which killed multiple worshippers. He then switched to an AR-15 style rifle and continued shooting inside the mosque as worshippers prayed.
 

After leaving the Al Noor Mosque, he drove to the Linwood Islamic Centre, arriving at 1:52 PM. There, he parked his vehicle, obstructing others from entering or leaving. Tarrant again opened fire, killing more worshippers both outside and inside the centre. He had planned to carry out further attacks but was arrested shortly after.

The police apprehended him at 1:59 PM, shortly after he fled the scene of the second shooting. In total, Tarrant killed 51 people and injured many more during his attacks across the two locations within a span of just a few minutes.