David Bagshaw had claimed the decision by authorities was improper and wanted a judicial review.
Bagshaw, of Toronto, was convicted of first-degree murder in the 2008 New Year's Day knifing death of 14-year-old Stefanie Rengel after months of taunting by his 15-year-old girlfriend, Melissa Todorovic.
She was also convicted of first-degree murder for badgering Bagshaw, in part by threatening to withhold sex, into killing Stefanie, a girl she barely knew but considered a rival.
Because he was just shy of his 18th birthday when he stabbed Stefanie, Bagshaw was tried as a young offender but sentenced as an adult to life imprisonment without parole eligibility for 10 years.
He began serving the sentence at the Sprucedale Youth Centre, but when he turned 21 in January last year, he was moved to Millhaven, an adult penitentiary.
Under Correctional Service of Canada policy, convicted murderers are placed in maximum security for the first two years of their federal imprisonment unless there are special circumstances.
In arguing against holding Bagshaw in maximum security, his lawyer John Hill said it would be "disruptive of the gains" Bagshaw had made at Sprucedale. He also noted the inmate "remains immature emotionally despite his chronological age."
Prison authorities, however, found no reason to give Bagshaw a break. They assessed him as a security risk given his belligerence and participation in violence while in youth custody.
An intake assessment found the need to put him in a "highly structured environment in which individual or group interaction is subject to constant and direct supervision."
Bagshaw did not help his own case.
In March 2011, he was charged with attempted murder for a knife attack on a fellow inmate at Millhaven Institution. Intervening prison guards shot him in the stomach and killed another inmate in their efforts to defuse the situation.
Bagshaw claimed to have been bullied into taking part in the attack — a tack he used at his murder trial.
In his recent ruling, Justice David Near dismissed Bagshaw's request for judicial review, saying authorities had acted properly in making the maximum-security decision.
At his trial, court heard how Bagshaw lured Rengel from the front door of her home. A short distance away, he stabbed her six times and left her to die in the snow.
Todorovic, who turned 20 in January, lost a separate bid late last year to remain in a youth centre for another year.