With 10 months before the election, Denis Napthine will announce the policy on Sunday, when he becomes the first premier to launch Midsumma, Melbourne's annual gay and lesbian festival.

The move will end decades of anxiety for countless men who were prosecuted before homosexuality was decriminalised in Victoria in 1981. Before decriminalisation, men who had consensual sex with other men were convicted of crimes such as ''buggery'' and ''gross indecency with a male person'', restricting them from travelling, volunteering or applying for jobs such as teaching.

With at least 100,000 people expected to attend Sunday's event, Dr Napthine will tell the crowd that ''these convictions have been allowed to stand for far too long'' and had stigmatised many people who had been forced to live with the burden of a criminal record.

''It is now accepted that consensual acts between two adult men should have never been a crime,'' Dr Napthine said. ''The Liberal government, led by Sir Rupert Hamer, recognised this and decriminalised homosexual sex in the 1980s. We also recognise the social and psychological impacts that have been experienced by those who have historical convictions for acts which would no longer be a crime under today's law.''

The changes follow similar laws recently introduced in Britain by David Cameron's Conservative government, which allow an estimated 16,000 convictions to be wiped from police records.

In Victoria, legislation will be introduced this year, paving the way for a showdown between the state Coalition and Labor over the so-called ''pink vote'', particularly in electorates such as Prahran and Albert Park.

Under the policy, anyone with a historical conviction for an offence relating to homosexual acts would be able to apply to have their conviction expunged, provided the offence is not a crime under current legislation.

The application would then be reviewed to ensure the offence related to consensual sex with a person of legal age. If determined the offence was no longer a crime under existing law, the record would be wiped clean. Convictions for non-consensual sex or sex with a minor will remain.

While there is little public data about the number of arrests and prosecutions that took place before homosexuality was decriminalised, experts believe thousands of convictions could have taken place given the era - a time when gays were often ''witch-hunted'' or entrapped by police.

Melbourne author Noel Tovey was one of the men convicted of having gay sex - or ''the abominable act of buggery'' as the offence was then called - in 1951, when he was 17. The former indigenous dancer was arrested after police raided a party in the Albert Park home of the female impersonator Max Du Barry.

Tovey, now 79, says he was coerced into confessing that he had sex with Du Barry (which he says was not true), spent months in Pentridge Prison awaiting a trial before being released with a good behaviour bond, and has lived with the stigma of a criminal record ever since.

While he was able to change his name and embark on a successful international career in theatre - he was raised as Noel Morton before learning the name on his birth certificate was Tovey, after his father - he admits other gay men weren't so lucky.

Opposition Leader Daniel Andrews has already promised to expunge historic gay sex convictions if he wins government at this year's November poll. Within Coalition ranks, Prahran MP Clem Newton-Brown has been lobbying Attorney-General Robert Clark for two years to change the law. ''At first I thought this might be a good symbolic gesture, however, after talking with Noel it became apparent that these convictions continue to impact on the lives of these men. Most have kept their convictions secret and the mental health impacts are enormous,'' Mr Newton-Brown said.

Human Rights Law Centre director Anna Brown said it was ''extremely pleasing to see the … government showing leadership on this issue.''

Labor spokesman Martin Foley welcomed changing the law, but said ''it sits uncomfortably'' with Dr Napthine's ''long-held opposition'' to gay rights.