He called the former Cuban leader "a giant among global leaders"
President Michael D Higgins has been criticised for his statement following the death of former Cuban leader Fidel Castro.
In a statement, the President expressed "great sadness" at the news, while Minister for Foreign Affairs called him "a dictator who presided over a questionable regime".
"He was a very divisive figure, embroiled in controversy for most of his career, and there will be very mixed views on his legacy."
Speaking to Newstalk, Micheál Martin agreed with Mr Flanagan's statement, though did not refer to the comments made by the President.
"There's no doubt Fidel Castro did undermine freedom of expression within his own country and he did lead a repressive regime", he said. "Ultimately, I think he created a country that did not grow economically and that was very challenging for the Cuban people."
Former Government Press Secretary Gerard Howlin believes President Higgins overstepped the boundaries.
Independent Senator Ronan Mullen described the President's statement as "fawning, offensive and wholly inappropriate".
A statement released on behalf of Renua said: “Whilst we understand the necessity to be tactful in speaking of the dead, particularly when the dead were recently leaders of other sovereign states, we do think it important to note that Fidel Castro was a dictator, and a brutal dictator at that.
“[His] regime murdered thousands of people, sentenced thousands of people to death, often following show trials, and engaged in the usage of torture, repression, the mass jailing of dissenters, sent homosexuals to labour camps to be ‘re-educated’ and declared that homosexuality was ‘incompatible with the revolution’.”
Leahy added: “It’s important that we remember that people suffered under Castro. An entire country suffered under Castro. The man destroyed the free press, jailed and tortured democrats, priests, homosexuals, and anyone who tried to stand against him.
"I, personally, cannot accept that the President speaks for me when he talks of him as a champion of the oppressed and the excluded, when he talks of him as if he was a normal politician who made a few minor mistakes. Fidel Castro murdered, tortured, and jailed all those who opposed him, and he should be remembered for his victims."
TD Thomas Byrne tweeted following the news:
RIP Fidel. But if Cuba was as brilliant as many on the left believe, why did millions flee, 100s of thousands of them on makeshift rafts.— Thomas Byrne (@ThomasByrneTD) November 26, 2016
Colm O'Gorman, the head of Amnesty International Ireland, highlighted Castro's mixed legacy on Twitter.
Some people seem to want to ignore Castro's horrific abuses of civil & political rights for some 50 years. Which were monstrous. 1/3— Colm O'Gorman (@Colmogorman) November 27, 2016
Some people seem to want to deny his delivery on social rights. Both are dishonest. Both are caught in blindness of personal ideologies 2/3— Colm O'Gorman (@Colmogorman) November 27, 2016
President-elect Donald Trump echoed Mr Flanagan's sentiments, calling him a "brutal dictator".
The former Cuban leader's death was announced yesterday. He died at the age of 90. Nine days of national mourning is currently underway in Cuba.