Taoiseach Micheál Martin said he was left with "no alternative" but to sack Barry Cowen after he refused to make a statement to the Dáil.
The former agriculture minister was sacked on Tuesday night after he refused to provide further public statements on his 2016 drink-driving offence.
Fianna Fáil's Dara Calleary has been appointed the new Minister for Agriculture. He had been chief whip for the last 17 days in the new Government.
Mr Martin told the Dáil that after reading the Garda file relating to Mr Cowen's drink-driving offence in 2016, he asked Mr Cowen to appear before the House to make a statement.
After Mr Cowen refused to do so, the Taoiseach said that in his view that was "not acceptable and tenable".
However, Sinn Féin president Mary Lou McDonald said that many were left "scratching their heads" about what happened in the hours after Mr Martin backed his then minister during Tuesday's Leaders' questions.
"People are wondering did you learn something new? Was there another twist in the tale, another piece of information?
"But actually the truth is that you knew this whole sorry story from the very beginning, not like the rest of us who learned of it piecemeal," Ms McDonald added.
Ms McDonald also said that Mr Martin "played down" the contents of the garda record.
Mr Martin said he first saw the garda file on Tuesday morning.
"I was fully satisfied yesterday that he should come in before the Dail," Mr Martin added.
"I made it clear to Deputy Cowen yesterday morning that he should come into the House. He said he wasn't going to, and I said I want you to reflect on that.
"As soon as Leaders' questions was over and the Dail was over, I contacted Deputy Cowen and said his position in refusing to come before the Dail, in my view, was not acceptable and tenable, and that he would have to come before the Dail.
"He still refused to go down that route and the fundamental difference between myself and Deputy Cowen on this issue is that Deputy Cowen took a legal route, a legalistic approach to defend his rights, in his words, as a citizen and as a public representative.
"In my view the issue could only be resolved through the political route and through coming into the Dail.
"In my view, a comprehensive statement was required."
Mr Martin said that while he does not want to prejudice the garda process, he has his "own view" on the record.
He added he was left with "no alternative" after Mr Cowen refused to make a statement to the Dail.
Labour leader Alan Kelly questioned how Mr Cowen received the file from the gardaí.
"You refer to it as a garda report or record, he refers to it as a Pulse file. Which is it?
"This is a subject Access Request Form. This is how you get information about yourself from An Garda Siochana. It usually takes between one and three months.
"How was this information provided to then-minister Cowen? Was it expedited for some reason?"
Mr Martin said he understood it is a Pulse file.
Social Democrat TD Catherine Murphy said: "The obvious question is, what occurred between two o'clock yesterday and 9pm last night?
"There was certainly no indication at Leaders' questions, in your response, that this would transpire the way it did."
Appointing Mr Calleary, Mr Martin said: "In his short time as Government whip, Minister Calleary has shown that he is very committed to not just reforming the Dail, but also in terms of overseeing a very comprehensive legislative programme."
Mr Cowen, who was in office for just 17 days, denies any allegation that he attempted to avoid a garda checkpoint in 2016.
He said he was "surprised and disappointed" by Mr Martin's decision to sack him and that it had also undermined his entitlement to fair process.
In a statement on Twitter he added: "Unfortunately the decision of the Taoiseach to remove me from office, when he supported me this afternoon in the Dail, has undermined and potentially prejudiced my entitlement to fair process."
Mr Cowen "adamantly denies" evading or attempting to evade a checkpoint on the night he was found to be drink-driving, and believes the Garda record is inaccurate.