The law should be changed to ensure the conduct of politicians can be investigated even after they leave office, the Fianna Fáil leader has said.
Micheál Martin also said that in his view the former Fine Gael TD Dara Murphy should face an inquiry.
Mr Murphy resigned on Tuesday following a controversy about his non-attendance at Leinster House while claiming a Dáil salary and expenses.
He has now taken up a position with the European Commission in Brussels, having spent much of the last two years working with the Fine Gael-affiliated European People's Party.
Neither the Standards in Public Office Commission (Sipo) nor the Dáil Members’ Interests Committee can investigate complaints about Mr Murphy because he is no longer a TD.
“Various mechanisms exist,” Mr Martin told The Irish Times, “but I think it’s not satisfactory what has happened this weekend. Ultimately I think the public are the ultimate decision-makers in terms of the politicians, and the politicians must be accountable to the public for their actions.”
In regard to Mr Murphy, he said: “he’s now not going before the people. I think the Taoiseach took a decision and Fine Gael took a decision to facilitate an arrangement with Dara Murphy which hasn’t been fully explained.
"I think it's an error of judgement on the Taoiseach's behalf – he was wrong to do that, [he was] essentially saying it's ok to work for Fine Gael in Europe for two years and ignore your Dáil duties and not have any parliamentary input for two years.
“That’s unacceptable in my view, and obviously there should be mechanisms there,” Mr Martin said, adding he believed Mr Murphy should have resigned from the Dáil in 2017 when he decided to work in Europe and that there should have been an acknowledgement from the Taoiseach that what happened was wrong.
Yesterday the Taoiseach told the Dáil he had spoken to Mr Murphy “about his remuneration and expenses” and the TD had confirmed he was willing to submit to any formal investigation regarding his conduct by the ethics committee or by Sipo, or to have his compliance examined by the Clerk of the Dáil.
Mr Murphy has insisted he was in compliance with the Dáil’s rules for the entire period.
Speaking to reporters in Derry, Mr Martin reiterated his view that Easter Sunday “marks a natural end to this Dáil” and there would be a general election shortly afterward.
"We did make a commitment in the context of the threat of Brexit and a no-deal Brexit to the island of Ireland that we would not create an instability or an incoherence while the negotiations were under way," said Mr Martin.
“The 31st of January is the new deadline in terms of the deal that’s on the table . . I’ve been honourable, I’ve put the national interest first - people didn’t think we would, we did, and I’m going to follow that through.
“There will be an election early in 2020 . . . I think Easter Sunday or the period up to Easter is the clear cut-off point, when the parliamentary session before Easter ends.
“We’re into a general election scenario then so we’re only talking a short while,” he said.
He said he did not have confidence in the capacity of Minister for Housing Eoghan Murphy, to deal with the homelessness crisis and said the Government has "failed in terms of housing and in terms of health".
Department of Housing figures released earlier this week showed the number of people living in emergency accommodation had risen to more than 10,000 at a time of year when such figures usually decrease.
The Fianna Fáil leader was in Derry with the SDLP leader Colum Eastwood, who is the party's candidate in Foyle in next week's general election. The parties entered into a partnership earlier this year.
Mr Martin addressed business leaders at a breakfast meeting and met representatives from Ulster University and Foyle Port before going canvassing with Mr Eastwood.
He said he found it “inexplicable and inexcusable that the Assembly and the Executive were collapsed when they were collapsed, and that they haven’t been restored at a time when the island of Ireland is facing its greatest threat through Brexit.”
Northern Ireland has been without a power-sharing government since January 2017, when it collapsed following a row over a botched renewable heating scheme.
Mr Martin said that it in his view this was a time of “great danger to Northern Ireland in terms of both the political vacuum and Brexit”.
He said the approaching Brexit deadline on January 31st “may concentrate minds”, but he believed that “what would be of great assistance to that would be a clear message from the ballot box that we want politicians who are prepared to take their seats and who are prepared to work.
“That, I think, would tip the balance in terms of the restoration of the Assembly and the Executive.”
