Ireland's incumbent president Michael D Higgins was elected to a second seven-year term in office, after winning a clear majority of votes, according to final results announced on Saturday.

After a successful campaign to re-elect Ireland's poet president, Higgins was officially declared elected to the Office of President of Ireland at Dublin Castle.

Higgins managed to win more than 800,000 out of 1.4 million votes on Friday's poll, according to state broadcaster RTE.

"People have made a choice as to which version of Irishness they prefer ... I will be a president for all of the people," Higgins said in a speech after the results were declared.

Prime Minister Leo Varadkar congratulated Higgins on Twitter for his near-certain win of the largely ceremonial office following Friday's vote.

A referendum on decriminalizing blasphemy by removing a reference to it from the Irish constitution that ran alongside the presidential election also won an overwhelming majority of support.

Broadcaster RTE reported that 65 per cent of voters had supported the change, while 35 per cent were against it. Turnout reached just 44 per cent.

Varadkar and his deputy, Foreign Minister Simon Coveney, had campaigned both for the re-election of Higgins and for changing the blasphemy law.

"We've already allowed for marriage equality, given women the right to choose [on abortion], and this is the next step," he said in an earlier video message on his campaign for the blasphemy referendum.

The premier had also called on voters to go to the polls, amid forecasts of a low turnout in contrast to Ireland's high-profile abortion referendum earlier this year, which saw countless emigrants returning home to vote.

Irish republican party Sinn Fein was the only political party to put forward a candidate, Liadh Ni Riada, to challenge Higgins. His other rivals, three of who were former panellists on the television show Dragon's Den, all stood as independents.