The botched renewable heating scheme was no justification to collapse the assembly, the Fianna Fáil leader has said.
Micheál Martin urged voters in Thursday's local government elections to choose politicians willing to return to power-sharing at Stormont.
"There never was a justification to collapse the executive, in my view," he said.
"I don't think the heating scheme was a good enough reason to collapse the executive on day one and I think the issues that are there can be resolved without necessitating the continued absence of an executive and assembly."
He joined SDLP leader Colum Eastwood canvassing voters in south Belfast ahead of this week's poll.
In February, SDLP members voted for a partnership with the Fianna Fáil in an effort to boost flagging electoral fortunes.
Mr Martin said: "There is an opportunity in the local elections and the European elections for people to let their voice be heard.
"I think people should indicate that they want people back in the institutions, back in the assembly, back in the executive.
"I would always be hopeful that people will see the light of day. Staying out does not work."
Former Sinn Féin deputy first minister Martin McGuinness's resignation early in 2017 in protest at the DUP's handling of the over-spending green energy scheme forced the collapse of the devolved institutions.
While same-sex marriage is a live issue between Sinn Féin and the DUP, the voters in the Republic overwhelmingly voted last year to legalise it.
Mr Martin said the issue was not weaponised in the Republic as a way to attack a political party.
"The assembly here should pass marriage equality, that would be the ideal way to get this resolved quickly," he said.
"The absence of an assembly and executive for two years or more has not helped marriage equality and has not brought it one step further."
Mr Eastwood said someone needed to legislate.
He suggested the petition of concern used to block contentious legislation be suspended and reformed while what he termed marriage equality could be delivered.
"Has there being no assembly delivered marriage equality? No it has not," he said.
"Has there being no assembly delivered anything around Irish language? No it has not.
"What has it done? It has led to longer waiting lists, schools being defunded, Brexit happening and us not there to do anything about it.
"That is the reality. The strategy that Sinn Féin has deployed has totally and abjectly failed. It may be time to think again."
