Judge Ronald Soloman told the court the fact Tupuolamoui had taken ecstasy and alcohol on the night of the bashing did not excuse his behaviour, the ABC reported.
Tupuolamoui sat in the dock with his head bowed as the sentence was read. He will be eligible for release in 2018.
Judge Soloman described the attack as "colossal'' and said that Mr Keohane, who had been working in Sydney, was "a successful and independent person who now has an uncertain future''.
Judge Soloman took into account Tupuolamoui's guilty plea but said it had to be considered that he had fled to Darwin after the bashing.
Isaako was sentenced in May last year last year to 19 years in jail with a non-parole period of 14 years for attempted murder over the bashing.
The 20-year-old was on bail for an unrelated aggravated robbery when he was arrested.