Agriculture Minister Dara Calleary is resigning from cabinet, effective immediately.
Mr Calleary apologised last night for his attendance at the event, which also included EU Commissioner Phil Hogan, multiple senators and independent TD Noel Grealish.
He said he "should not have attended" the event at a hotel in Galway, which took place just 24 hours after the new Covid-19 measures were introduced.
Last night I attended a function I committed to a number of weeks ago, to pay tribute to a person I respected and admired greatly. In light of the updated public health guidance this week I should not have attended the event. I wish to apologise unreservedly to everyone 1/2— Dara Calleary (@daracalleary) August 20, 2020
It is understood that Taoiseach Micheál Martin was "furious" about the event, which came just 24 hours after new Covid-19 guidelines were announced.
Current public health guidelines say that no more than 50 people should gather indoors.
An Garda Síochána has confirmed it is investigating the event.
"An Garda Síochána is investigating an event that was held in Co. Galway on the 19th August, 2020 into alleged breaches of The Health Act 1947 (Section 31A-Temporary Restrictions) (COVID-19) (No.3) Regulations 2020, as amended.
As this is an active investigation An Garda Síochána has no further comment."
The Agriculture Minister's resignation letter read as follows:
In a statement issued this morning, Taoiseach Micheál Martin said that Mr Calleary's attendance at the golf event was wrong and that he has accepted the Minister's resignation:
"This morning Deputy Dara Calleary tendered his resignation as Minister for Agriculture, Food and the Marine, following his attendance at the Oireachtas golf dinner on Wednesday evening.
"His attendance at this event was wrong and an error of judgement on his part. I have accepted his resignation.
"Dara Calleary, since he was first elected to Dail Eireann has been, and remains, a committed and dedicated public representative.
"This error of judgement was out of character. He has made the right decision for the country, particularly in the light of our continued efforts to supress Covid-19."
Earlier, Sinn Féin's housing spokesman Eoin Ó Broin told Newstalk Breakfast the Dáil should be reconvened "as a matter of urgency".
"I have to say it's just another example of the dysfunction at the very heart of this Government.
"We've had this week a not-so private row between the Taoiseach and Tánaiste, we've had the most hastily announced set of restrictions measures, huge contradictions.
"We've had Government departments contradicting each other, we've had the minister for health contradicting Government departments.
"And now we have not just one minister, but possibly other senior politicians and former politicians breaching both the old and the new rules.
"What we need is we need the Dáil to be convened as a matter of urgency.
"And we need Micheál Martin and Leo Varadkar not only to make statements on all of these issues, but to take questions.
"And that needs to happen as quickly as possible."