Eamon Ryan has retained his position as Green Party leader by 48 votes.
Mr Ryan faced off with his long-time deputy leader, Catherine Martin, in a postal vote, winning by a tight margin.
Mr Ryan received 994 votes to Ms Martin's 946.
A total of 1,950 of 2,923 eligible members voted in ballot, the party turnout was 66.7%, with 10 spoiled votes.
Mr Ryan said he was "very glad" to be re-elected after a "civil" competition and "very honoured" by the result.
"It's a really close result, numbers are tight, and could've went either way, I will reflect on that," he said.
The winner of the Green Party Leadership Contest was announced this evening via live broadcast to the party membership. Of a valid poll of 1940 votes, Catherine Martin received 946 votes and Eamon Ryan received 994 votes.— Green Party Ireland (@greenparty_ie) July 23, 2020
Eamon Ryan will continue as leader of the Green Party. pic.twitter.com/p0mDyfC50O
"It's tough times in the country at the moment, and tough for us in government and we have a responsibility to serve our people, and our party is fit for that.
"I'm committed to doing everything I can to try and help this party and help our people in a remarkably challenging period.
"We must engage with our people in the same way as this election, be open and transparent."
The win was bittersweet as the party had undergone a day of very public resignations from members including former MEP candidate Saoirse McHugh, who called the party "toxic", while a number of others publicly stated they would also be leaving the party.
Thread on leaving the greens:— Saoirse McHugh (@saoirse_mchugh) July 23, 2020
I have left the Green Party. I doubt that’s a surprise to most people.
The reasons I have left are obvious, I joined the greens with the hope of furthering the cause of climate justice..1/
The resignations came after months of fighting within the party membership and allegations of harassment and bullying after a split formed during programme for government negotiations.
Ms Martin congratulated Mr Ryan, noting he led the party to their greatest electoral success and said it must now "unite after the divisions it has experienced in recent months".
"This is an important and testing time as Greens, we've embarked on a government by facing extraordinary challenges," she said.
"As Eamon leads up forward, the most important thing we can do is stay together, stay united.
"There will not be an easy time ahead and we will need strong leadership.
"Stick with us, whatever we have to weather, we will weather it together".
She added that the party was "losing good people" and needed "reform in some way", before refusing to rule out running for the leadership again in the future.
One supporter of Ms Martin's, who sits on the party's executive council, said they were expecting more resignations in the wake of Mr Ryan's win.
"We were expecting it to be very tight, we knew she had a small chance but that Eamon was the favourite," they said.
"A lot of people are not that happy, fairly disappointed, but we ran a good campaign.
"I expect a lot more people will leave, a lot of people stayed and voted for Catherine even though they thought they were going to leave, a lot of people are in difficult positions, so they maybe won't leave tomorrow but I'm expecting a lot more in future, and if Catherine was leader they might have stayed but who knows."
Due to the narrowly tight margin of the ballot, it has already been suggested that it is unlikely Mr Ryan will lead the party for a further five years.
"I suppose he's entitled to be leader for the next five years, that's his decision, it's up to him," the source said.
"I think he does have the appetite for it, although he mentioned during the campaign he said: 'the next couple of years', he didn't commit to the full term."
Mr Ryan has said he is "open" to the idea of having a co-leader in the future, which could be proposed at the party's next national convention.