Attorney-General Elise Archer announced she will table a bill including the same offences and same minimum sentences as one that was defeated in the upper house in 2020 - the second time it had failed to pass parliament.

The bill proposed a mandatory minimum of four years' prison for the rape of a victim under 17 and four years for maintaining a sexual relationship with a young person where rape has occurred.

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Other minimum sentences would be three years for maintaining a sexual relationship with a young person under aggravating circumstances, and two years for sexual intercourse with a young person under aggravating circumstances.

The law proposals faced extensive opposition from legal groups including the Law Society, Bar Association and the Director of Public Prosecutions, and was not supported by Labor or the Greens.

Ms Archer said the government had taken the policy to three elections and would be making another attempt as a result.

"We have received a strong mandate each time - only for Labor to inexplicably vote against on every occasion," she said.

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The announcement came days after victims' advocate Steve Fisher raised concerns about a Devonport woman who received two years' jail - one year suspended - for the persistent sexual abuse of a 13-year-old boy.

He said it appeared the government was responding to this specific sentence, and he would be lobbying Tasmanian politicians to pass the laws this time.

"I would be absolutely disgusted if it doesn't happen this time. The bill must have tripartisan support," Mr Fisher said.

The government commissioned a report from the Sentencing Advisory Council in 2016, which recommended mandatory sentencing not be introduced in Tasmania.

The report based this upon "no supporting evidence" that minimum sentences were a deterrent to committing crime, would deter offenders from pleading guilty and result in more victims having to give evidence at trial, and placed more discretion with the DPP instead of judges.

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The Bar Association supported increasing maximum penalties to give judges greater discretion in sentencing, a policy which Labor supports, but Ms Archer described as "ill-informed".

Labor justice spokesperson Ella Haddad said the opposition would continue to rely on advice from legal groups and those within the sector.

"I dare say you would struggle to find a member of the judiciary who would support mandates in any area of sentencing, but of course tying mandatory sentences to an area of offending as grotesque as child sex offending certainly gives you the political edge that you are perhaps after in this debate," she said.

Greens justice spokesperson Rosalie Woodruff said she was concerned the laws would unreasonably tie up Justice Department staff when their focus should instead be on improving protections for children, as per the Commission of Inquiry.

In 2020, the Commonwealth - with the support of Labor - passed laws for mandatory minimum sentences for child sex offenders.

The Tasmanian laws will be tabled by the end of this year.

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