Catherine Connolly, a veteran lawmaker on the far Left of the Irish political spectrum, was elected president by a landslide margin on Saturday.
Connolly, 68, an independent candidate backed by the entire left-dominated opposition, has previously stated that Hamas is "part of the fabric of the Palestinian people," and has described the war in Gaza as a genocide.
"Both sides have committed war crimes," she said of Israel and Hamas in September.
"[Hamas] were elected by the people the last time there was an election. Overwhelming support for them back in 2006 or 2007. They are part of the civil society of Palestine. We're reliant on them for figures in relation to the deaths."
She also said that Israel was acting like a "terrorist state' and that she had "utterly condemned" Hamas "over and over."
Left wing-lawmaker who said Israel acted like a terror state wins Irish presidency
Connolly was elected after winning 63% of the first preference vote for the largely ceremonial role.
Connolly, a long-time critic of the European Union in overwhelmingly pro-EU Ireland, backed by the left-dominated opposition, was not a household name and was underestimated by many at the start of the contest for the largely ceremonial role.
Connolly, an independent candidate, built momentum as the campaign progressed, enthused younger voters, and was elected with 63.4% of the vote. The other candidate seeking election, ex-cabinet minister Heather Humphreys, won 29.5%.
"I will be a president who listens, who reflects, and who speaks when it's necessary. Together we can shape a new republic that values everybody," Connolly said in a speech at Dublin Castle.
Ireland's president is largely a figurehead, with seldom-used powers to test the constitutionality of legislation, but often speaks on the global stage and welcomes other heads of state to the country.
Many of Connolly's views - from denouncing the EU's plans to boost military spending to questioning the trustworthiness of the United States, Britain, and France over their stance on the war in Gaza - are well to the left of many of the parties backing her, as well as outspoken incumbent Michael D Higgins.
The former clinical psychologist and barrister is also one of the leading pro-Palestinian voices in parliament - a stance shared by the government and most voters.
Although Connolly served as deputy speaker of Ireland's lower house after being first elected in 2016, her win was widely viewed as continuing the recent trend of choosing a more independent president based on the candidate's values.
She also benefited from dire campaigns from the two governing parties. Humphreys was not Fine Gael's first choice. Fianna Fail's pick, former Gaelic football coach Jim Gavin, abandoned his bid due to a financial scandal.
The result was a boost to hopes among the previously divided left-wing opposition, led by Sinn Féin, of building a bloc capable of ending their center-right rivals' century-long grip on power.
Political analysts caution that such cohesion will be more challenging when the parties are in competition in a parliamentary election due by 2030. An Ireland Thinks polling-day survey found only 51% of Connolly voters would vote for a left-wing alliance.
Labour Party leader Ivana Bacik said on Saturday the center-left party would have issues with a coalition led by Sinn Féin.
A record 13% of voters also spoiled their votes, partly due to a planned protest by supporters of a conservative campaigner who failed to secure the required support from elected representatives to make the ballot.
Prime Minister Micheal Martin said the government was open to reforming the nomination process.