A Tokyo District Court panel of six lay judges and three professional judges convicted Richard Hinds of strangling Furlong at the Keio Plaza hotel on May 24, 2012, the Irish Independent reported.
Presiding Judge Masayuki Ashizawa described the crime as "atrocious and vicious" and said the fact that Furlong was "strangled with force for several minutes" showed murderous intent.
Hinds, from Memphis, argued throughout his two-week trial Furlong had voluntarily gone to the hotel with him and willingly engaged in "rough sex," the Irish Times reported.
The sentence he received was the maximum allowed under Japanese law because he is a minor.
"It's not enough, given the pain he caused Nicola," said Angela Furlong, the victim's mother.
Furlong, from County Wexford, was spending a year at a Japanese University at the time of her slaying.