The party is on 21% with its new leader's satisfaction rating at 51%
Mary Lou McDonald is almost as popular as the Taoiseach Leo Varadkar.
A Behaviour and Attitudes poll in the Sunday Times brings a big boost for both Sinn Féin and its new leader.
The party is on 21%, an increase of two points on top of a three point rise last month.
Ms McDonald's satisfaction rating is up by five points to draw level with Fianna Fáil leader Micheál Martin on 51%.
This is within two points of Leo Varadkar, who is on 53%.
But Mr Varadkar saw a fall in his personal satisfaction rating - down six - while Mr Martin's fell four.
Support for Fine Gael is up one to 33%, eight points clear of Fianna Fáil, who have dropped two to 25%.
The Green Party and Solidarity/PBP are unchanged on 2% and 1% respectively.
The Independent Alliance is down one to 2%, while the Social Democrats move up to 1%.
Renua also has 1% support, while Independents and others are down two to 10%.
The paper notes Sinn Féin's gains have come largely at the expense of smaller parties on the far and centre left and independents.
Sinn Féin support has also grown six points in Dublin, and is up five points among women voters to 22%.