She is among four Ministers and four TDs who added their support to Mr Varadkar's campaign to succeed Enda Kenny during the day.
Others in the ministerial ranks to back the Social Protection Minister were Joe McHugh, Minister for the Diaspora and International Development, who joined Mr Varadkar in Gweedore, Co Donegal, last weekend, and Eoghan Murphy and Sean Kyne.
"He has also made a substantial contribution to Limerick, and as minister I found him to be a constructive and supportive colleague in Cabinet".
But Minister Coveney says despite this the campaign isn't over yet.
"He has much to contribute yet and I do hope that he will continue to play a role in Irish and European public life and in the Fine Gael party long into the future".
Helen McEntee, another junior minister in Mr Varadkar's camp, said: "Look at the fresh new approach he has taken to politics, look at how he interacts with people, look at his vision for a more forward-thinking and open Ireland".
He said that Minister Varadkar has a "vision of a resilient and competitive economy" that can support a fairer Ireland.
Mr Varadkar sought to set a strong early pace by organising a large number of declarations for his candidacy.More news: Dollar heads for worst week in over a year amid political uncertainty
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In what is expected to be a two-horse race, nearly 21,000 Fine Gael party members will vote at 26 polling stations from May 29 to June 1, and the parliamentary party, which includes 73 TDs, senators and MEPs, will vote in Dublin on June 2.
The contest will be decided using a weighted voting system across three electoral colleges - the parliamentary party, councillors and party members.
Minister for Foreign Affairs Charlie Flanagan, meanwhile, declared his intention to support Mr Varadkar saying he was the "change candidate".
Mayo's third Fine Gael senator, John O'Mahony, is reported to be backing Minister Simon Coveney for the post.
MICHAEL Noonan is to step down as Minister for Finance and will not seek a seat in the next General Election nor will he seek a seat at the next cabinet table..
He understands, as he said last week, the unique circumstances of Donegal, cut off from the rest of the North for most of the last century by partition, and cut off geographically and in other ways from the rest of the State.
The Taoiseach has resigned as leader o the Fine Gael party.