Out of 1,000 people questioned in the Red C survey, 53% said they would vote Yes in the 31 May referendum, up six points on the last poll two weeks ago.
The poll suggests 31% would vote No, down four points, while 16% were undecided, down two points.
The referendum will decide Ireland's support for the treaty, designed to tighten budgetary rules across Europe.
Those advocating a Yes vote say the treaty will bring stability to Ireland's bailed out economy, while those on the No side believe it would mean years of further austerity.
Only the Czech Republic and the United Kingdom refused to sign up to the pact.
In terms of party support, the poll commissioned by the Sunday Business Post suggested that Taoiseach Enda Kenny's Fine Gael party has dropped three points to 29%, while coalition partner Labour is down to 13%.
Fianna Fail is up two points to 19%, while Sinn Fein is also up two to 21%, the party's highest ever rating in a Red C survey.
Independents and others are unchanged at 18%.
Support for the Irish Republic signing the fiscal treaty has increased, an opinion poll has suggested.