Sinn Féin has made a gain of six percentage points in the latest Behaviour and Attitudes poll for the Sunday Times.
The party now stands at 20% for the first time since April.
Fianna Fáil has retained the lead at 29% but it's down a point on last month, while Fine Gael's support is steady at 26%.
The Greens are on 5% and Labour is at 3%, both down two points.
The Social Democrats, Solidarity-PBP, and Renua have one% each.