Australian Prime Minister Tony Abbott says there will be a very full, frank, candid and decent debate inside the Liberal partyroom about legalising same-sex marriage.

Abbott has told reporters in Canberra it's an issue where decent people can differ and at some point, nearer to a vote, Liberal MPs would debate the issue in their party room.

Labor leader Bill Shorten says the time is right for marriage equality in Australia.

Shorten has told the Seven Network Australia needs to move forward and catch up with the times.

A vote on same-sex marriage in federal parliament is looming, with Labor to move a bill next week and MPs predicting legislation will pass by the end of the year.

Prime Minister Tony Abbott has declined his frontbenchers a free vote, leading to the defeat of Labor private legislation in 2012.

But the recent success of a same-sex referendum in Ireland has led to calls to act in Australia.