Stephen Anderson was born in Wellington, New Zealand, around 1972–1973, to Neville and Helen Anderson. He grew up in the suburb of Khandallah, enjoying a comfortable upbringing with his family. Stephen developed an early interest in the outdoors, often going on hunting trips with his father, which fostered his familiarity with firearms.

In the mid-1990s, Anderson pursued a career in dental technology, completing a diploma and working in a dental laboratory. However, during this period, he began experiencing mental health issues. In 1995, he was diagnosed with paranoid schizophrenia after an incident involving the police. Despite being prescribed antipsychotic medication, Anderson was non-compliant with his treatment and also used cannabis regularly. His mental health deteriorated over the following years, leading up to the tragic events in 1997. ​

On the morning of February 8, 1997, at the Anderson family's ski lodge in Raurimu, New Zealand, Stephen Anderson, then 24 years old, carried out a mass shooting. During breakfast with family and guests, Anderson left the table, retrieved a 12-gauge sawn-off shotgun, and returned to the dining area. He first shot his father, Neville Anderson, and then proceeded to shoot others present, killing six people and wounding four. The victims included his father, four family friends, and a neighbor.

Anderson fled the scene and was later apprehended by police, found naked in a nearby field. He was charged with six counts of murder and four counts of attempted murder. In December 1997, the High Court in Hamilton found him not guilty by reason of insanity, and he was committed indefinitely to psychiatric care at Porirua Hospital. ​

Over the years, Anderson was granted limited release and eventually discharged from the hospital in 2009, living under community supervision. He has since expressed remorse for his actions, attributing them to his untreated mental illness at the time. In 2023, he published a memoir titled "The Devil's Haircut: My Life Before and After the Raurimu Massacre," offering insight into his experiences and the events leading up to the tragedy.