Mr Garrett, who led the part' />
Act's law and order spokesman, MP David Garrett, was convicted of assault in 2002 in Tonga, he confirmed last night.
Mr Garrett, who led the party's "three strikes" policy on tougher sentencing for serious violent offences, has not publicly disclosed his conviction.
But Act leader Rodney Hide said Mr Garrett had disclosed it to him before he joined the Act list at No 5 for the 2008 election.
He did not believe Mr Garrett had committed assault and said he preferred to judge him on his "outstanding" record as an MP.
Mr Garrett issued a statement giving his version of events after TV3's Campbell Live last night revealed the conviction.
Mr Garrett, who worked as a lawyer in Tonga, said he was attacked outside a bar in Nuku'alofa by Dr Mapa Puloka, head of psychiatry at the local hospital.
Campbell Live claimed the altercation was over Dr Puloka's former wife.
Mr Garrett said his own jaw had been broken in two places after he was attacked from behind.
He had returned to Middlemore in Auckland for treatment and then laid a complaint with the Tonga police. After Dr Puloka was charged with assault, he in turn laid a complaint of assault against Mr Garrett.
Mr Garrett denied the assault and produced two witnesses, the bar's bouncers, at the trial but was convicted and fined $10.
He had immediately lodged an appeal and has yet to be given a reason as to why it has been delayed.
Dr Puloka was fined $100.
Mr Hide said he accepted Mr Garrett's word that he had not assaulted the other man.
He had worked on oil rigs for 10 years and had turned his life around.
Mr Hide said Parliament was "a house of representatives. It's not a house of saints."
Dr Puloka could not be contacted last night.
Many MPs have minor convictions but Mr Garrett's non-disclosure is more relevant because crime is the primary focus of his parliamentary career.
In his maiden speech in December 2008, he even talked about common assault, drawing attention to the fact that Elton John's manager had served a month in Mt Eden Prison in 1974 - "not a month of home detention or 10 hours' community work".