Ms Harney, who earlier that day attended a Public Accounts Committee (Pac) hearing about funding issues in University of Limerick, was among around 200 attendees at the dinner to raise funds for the current Tánaiste’s political war chest.
Ms Harney, who is director with a host of firms in the healthcare, pharmaceutical and accountancy sectors, is also the Chancellor of University of Limerick.
She was before the Pac to discuss the controversial purchase of an old Dunnes Stores site by the university.
The former Progressive Democrats leader is a long-standing friend and confidante of Mr Varadkar.
Another former tánaiste, Frances Fitzgerald, was also at the event in the luxury Castleknock Hotel. Ms Fitzgerald served as justice minister and tánaiste when Mr Varadkar was first elected taoiseach.
A number of public relations and lobbying firms including Edelman, Q4 and Heneghan were represented at the event and this included former political advisers who went on to work in the private sector.
There were also a number of members of the Law Library present at the dinner.
One Fine Gael source said the barristers who would show up to these dinners were “all jockeying to be the next attorney- general”.
Mr Varadkar told the fundraising dinner that Fine Gael had to be able to match Sinn Féin financially on the ground.
He said Fine Gael coming up against a well-resourced opposition at the next general election was a theme of the speeches at the dinner.
In an invitation for the fundraiser, guests were told by Mr Varadkar it is “essential that Fine Gael retains and strengthens its position” so the country does not “jeopardise all that we have gained by giving way to populism”.
Donors were offered beef or fish on the menu.
Mr Varadkar showed he is not a natural at hosting dinners at the event, according to one guest.
“Leo is terrible at these events, he doesn’t work the room at all. He doesn’t do a tour of the tables. He just hangs out with his own pals,” the political source said.
The dinner sparked speculation before the event about a possible early general election but a weekend opinion poll did not spell good news for Fine Gael, which dropped five points to 19pc. Mr Varadkar’s personal approval rating was up two points.
Meanwhile, Sinn Féin was up four points to 36pc, while Fianna Fáil was up a point to 24pc and Greens were down two to 2pc.