The results also suggest that Michéal Martin is the most popular of the party leaders
An opinion poll in today's Irish Times shows support for Fianna Fáil is at its highest point in the last eight years.
Micheál Martin's party has a 33% approval rating - nine points ahead of Fine Gael.
The poll of 1,200 voters, conducted by Ipsos/MRBI, was taken on Monday and Tuesday of this week amid both the abortion and Brexit controversies.
Compared to the general election result, support for Fine Gael dropped two points to 22%. In contrast, Sinn Féin support increased two points to 16%.
The poll also shows that support for Labour continues to fall - now at 5% - and there has been a big drop off in support levels for Independents & others (22%, down 8% compared to the election).
A separate opinion poll published at the weekend showed a massive drop in support for Independents.
Of the smaller parties, the Greens have the highest level of support at 4%.
Meanwhile, the Irish Times' results today also suggest that Michéal Martin is the most popular of the party leaders, with satisfaction rating of 43%. That puts him ten points ahead of Enda Kenny's rating and 12 points ahead of Gerry Adams.
New Labour leader Brendan Howlin has a satisfaction rating of 26%. Overall satisfaction in the Government sits at 31%.
Pat Leahy, Deputy Political Editor with the Irish Times, spoke to Newstalk Breakfast about the result.
"For many people who deserted Fianna Fáil in 2011, they were lifelong Fianna Fáil voters and their desertion was only going to be temporary," he explained.
"I think the second reason is that Michéal Martin has convinced many of the voting public that his party has learned the lessons of past mistakes. And I think the final reason, in general, they approve of what he has done post-election," he added.