Brett Peter Cowan was born on September 18, 1969, in Bunbury, Western Australia. He was the third of four boys in the Cowan family. His mother, Marlene, was a homemaker and worked for the RSL, while his father, Peter Cowan, was a Major in the Australian Army and a Vietnam veteran. The Cowans had a strict household and raised their children in the Catholic faith. Many people described them as a "good family." However, Peter Cowan was often away due to his Army duties and suffered from PTSD.

In the early 1970s, the family moved to Brisbane, Queensland. They settled in a suburb called Everton Park. Cowan and his brothers attended Marcellin College, which is now known as Mt Maria College. His year nine English teacher noted that Cowan sometimes bullied other students. Some classmates remembered him as ordinary, stating he didn't have many hobbies or social interests.

Cowan dropped out of school in year ten. After that, he worked various odd jobs during his late teens but could never stay in one job for more than a few months. He faced difficulties accepting his bisexuality and was known to be challenging for his mother. She described him as a "handful" as a child and difficult as a teenager. Cowan began to involve himself in petty crime, and by age 17, he had his first criminal conviction. During this time, he regularly used drugs like LSD, cocaine, and methamphetamines.

As a child, Cowan was also part of the Boys Brigade, a youth organization that focuses on character development and community service. However, as he grew older, his behavior became more problematic. Cowan occasionally stole from his mother, which added to their troubles. He later admitted that drug use affected his decisions and boundaries.

On December 7, 2003, 13-year-old Daniel Morcombe disappeared after leaving home to catch a bus. He planned to go to a shopping center for a haircut and to buy Christmas presents. During a brief period, he was allegedly abducted by Brett Peter Cowan, who lived nearby. Following Daniel's disappearance, Cowan was investigated but denied any involvement.

Years later, Cowan became a key suspect again. In April 2011, undercover police used a special operation called Mr. Big to gain his trust. During this operation, Cowan eventually confessed to abducting Daniel and led police to the location of his remains. On August 13, 2011, Cowan was arrested.

In March 2014, Cowan went on trial for the murder of Daniel Morcombe. He faced multiple charges, including child stealing and interfering with a corpse. After a lengthy trial, Cowan was found guilty of all charges. On March 14, 2014, he was sentenced to life in prison, with the possibility of parole after 20 years.

Cowan had a history of previous sexual offenses against children, with convictions dating back to 1987 and 1994. These prior crimes influenced the severity of his sentence in the Morcombe case. Throughout the trial and his evaluations, Cowan was described as a pathological liar with serious psychological issues. He continues to serve his sentence in prison.