Phil Hogan says his travel to and from Kildare while it was in lockdown was to collect "essential work papers."
He also confirms he was stopped by An Garda Síochána for using a mobile phone while driving during the same trip on August 17th.
Kildare has been in lockdown since August 8th.
Mr Hogan arrived in Ireland on July 31st and says he completed the statutory Passenger Locator Form.
He then travelled to his residence in Co Kildare and was admitted to a Dublin hospital for a medical procedure on August 5th.
He says while in hospital, he tested negative for COVID-19 and claims that a negative test result "ends the self-restriction period".
He references a Citizens Information web page for this - however the HSE advice does not include such a clause.
The Citizens Information Board has moved to clarify the issue.
It says the web page Mr Hogan refers to is for those who have been told they are a close contact of a confirmed case.
— citizensinfo (@citizensinfo) August 25, 2020
It says it does not apply to people who have arrived in from overseas, and there is another page for that.
The board adds that its website is not funded by the HSE and is not an official Government source.
On August 6th, Mr Hogan was discharged from hospital and returned to Co Kildare.
The next day he says he travelled to Kilkenny before the local lockdown rules came into effect at midnight.
While on August 12th he travelled to Dublin from Kilkenny for "essential work reasons", which required his attendance at the European Commission office.
On August 13th he says he "played golf in Adare, Co Limerick" and returned to Kilkenny.
He then says he travelled from Kilkenny to Galway on August 17th and "stopped briefly" in Kildare at the property he had been staying to collect "some personal belongings and essential papers" relating to ongoing negotiations with the United States Trade Representative, Robert Lighthizer.
Mr Hogan explains: "I believe that this constitutes a reasonable excuse for entering the county under the COVID regulations.
"It was during this journey I was stopped by a member of the Irish police who had seen me holding a phone while I was driving.
"The policeman cautioned me against holding a phone and there were no charges or further actions under the road traffic legislation.
"I very much regret having answered the phone while driving."
He says he was an invited guest to an Oireachtas Golf Society event on August 19th and "was assured by the organisers and the hotel" that it was being held in full compliance with all relevant COVID-19 rules.
"I had no reason to question or doubt that assurance, particularly in circumstances where an Irish Government Minister was attending and speaking at the event", he says.
He played golf in Clifden that same day.
On August 21st he says he returned from Galway to his residence in Co Kildare to collect personal belongings, including his passport, and stayed there overnight to catch an early morning flight to Brussels.
Referring to the Oireachtas Golf Society dinner, he adds: "I fully accept that it is abundantly clear that the event should not have been held and that I should not have attended this dinner.
"I accept this and have made a full apology to the Irish people for having done so."
Mr Hogan told the Financial Times he hoped he would stay in charge of EU trade policy.
However he said this is ultimately a decision for EU Commission President Ursula von der Leyen.
"I'm hoping that she will accept this report as a sound and solid basis for allowing me to continue in the trade portfolio and as a commissioner but that's a matter ultimately for her to decide", he said.
"I feel that I have given enough information about how I have fully complied with these regulations in Ireland to my boss, the president of the European Commission", he added.
This story has been updated. Read more here