The Supreme Court has rejected a seven-year prison sentence for a mentally ill man convicted in 2018 of trying to kiss a stranger on a Wellington street without her permission.

Daniel Clinton Fitzgerald's sentence - which has attracted plenty of attention over the years because of its reliance on the controversial three-strikes law - will now return to the High Court for him to be sentenced "in accordance with ordinary sentencing principles".

When Fitzgerald was initially sentenced, Justice Simon France pointed to the defendant's schizophrenia and acknowledged that such a crime would not usually result in prison time. But his hands were tied by the law, he indicated.

Seven years was the maximum possible penalty for indecent assault, the result of Fitzgerald making unwanted contact with the woman's cheek as he struggled with her on Cuba St.

Fitzgerald, who had two prior convictions for serious violent offences, also pushed the woman's friend against a shop window when she tried to intervene, according to court documents.

Labour attempted in 2018 to repeal the three-strikes law, which was put in place by the previous National government, but the effort was stymied by New Zealand First.

For the past three years, Fitzgerald's sentencing appeal has made its way through the courts. The Court of Appeal upheld the sentence in July 2020, despite judges acknowledging it was "disproportionately severe" and breached his rights.

Justices David Goddard and Denis Clifford wrote last year that they tried to "identify a tenable reading" of the law that would allow the mandatory sentence to be avoided.

"We have reluctantly concluded that this course is not open to us," they said.

The Supreme Court issued its ruling on Thursday afternoon.