Martin Schulz of the SPD party insisted "we will push through marriage equality in Germany"
The German parliament will vote on legalising same-sex marriage this week.
It comes after the government's junior coalition partner the Social Democrats (SPD) backed a push for a vote by left-leaning parties.
SPD chairman and former European Parliament president Martin Schulz insisted that the law would be passed this week.
We will push through marriage equality in Germany. This week.— Martin Schulz (@MartinSchulz) June 27, 2017
Chancellor Angela Merkel, meanwhile, signalled a change in her approach to the issue.
While her conservative Christian Democrats (CDU) have previously opposed the prospect, earlier this week Mrs Merkel suggested such a vote could be a "question of conscience" for individual members of parliament - meaning MPs would no longer have to follow a party line.
A vote on the issue is now scheduled to take place in the Bundestag on Friday, and is expected to pass.
The Local reports that the push for a vote has caused a "serious conflict" in government, as the CDU were opposed to a marriage equality vote before the upcoming national election in September.
The German Green party, one of the groups backing the legislation, argues there is "no conceivable reason why the state denies same-sex couples the right to marry".
Citing equality legislation introduced back in 2001, the party adds that “after 16 years, it is finally time for marriage for all”.
As well as Ireland, countries such as France, Portugal, Spain and the UK allow same-sex marriage, leaving Germany one of the few Western European countries to have not introduced marriage equality.
Gay couples in Germany are currently allowed enter civil unions, but do not have all the rights guaranteed to married couples.
According to The Local, the new legislation - if passed - would allow same-sex couples to jointly adopt children.
Polls have shown a vast majority of Germans support same-sex marriage.