Sinn Fein's first act in the next Assembly term will be to propose legislation to allow same-sex marriage in Northern Ireland.
Highlighting the issue as a priority for his party, Martin McGuinness insisted he did not want to be part of a region considered "backward".
Outlining Sinn Fein's manifesto for May's poll, Mr McGuinness also pledged to pursue legislation to enable abortion in cases of fatal foetal abnormality, claiming rival Assembly parties which had "run away" from the contentious issue would have "no hiding place" in the new mandate.
Same-sex marriage has been rejected five times by members of the devolved legislature.
Although the majority of Assembly members voted in favour of introducing gay marriage when it was debated for a fifth time last year, the proposal fell because unionists who opposed the move deployed a controversial voting mechanism to veto it.
Following the Yes vote in last May's referendum on marriage equality in the Irish Republic, Northern Ireland is the only part of the UK or Ireland where civil marriage is denied to same-sex couples.
Mr McGuinness declared his party the "most progressive" in the Assembly as he outlined a 10-point programme to the electorate. He said the issue of same-sex marriage had to be addressed, claiming people in the lesbian, gay, bisexual and transgender (LGBT) community had been treated like "second-class citizens" for too long.
"We don't want to be part of a backward region, we want to be part of region that is known to stand up for the rights of people who feel that they are being discriminated against."
In past marriage equality debates, the DUP has tabled a petition of concern voting mechanism that effectively blocks any proposal which is opposed by 30 or more of the 108 Assembly members.
At the election manifesto launch in Londonderry's Playhouse theatre, Mr McGuinness said he hoped the Assembly could reach a point where petitions of concern were deployed in "very rare circumstances".
Abortion laws are far stricter in Northern Ireland than in the rest of the UK, with terminations only permitted when a mother's physical health or mental well-being is at risk.
A bid to enable abortion when there has been a diagnosis of fatal foetal abnormality (FFA) was defeated earlier this year. DUP Health Minister Simon Hamilton instead set up a working group to examine the issue.
Mr McGuinness has left his Mid Ulster constituency to run in his native Foyle in this election. It is part of a Sinn Fein strategy to overtake the once dominant SDLP in the constituency.
Mr McGuinness yesterday said his party could take three seats in next week's vote.