Mr Casey hinted he might now turn his focus to securing another elected office, potentially in the Dail.
Higgins received 55.8 percent of the vote on Friday, and the results were quickly contested by other six candidates.
65 percent of the population, and every constituency, voted to pass the referendum, with 35% against.
Opinion polls had Mr Casey, who lives in Donegal, on 2% but following on from controversial comments about those on social welfare and the traveller community his national popularity rose to 20%.
Following a referendum on Friday, 65 percent of voters agreed to change the medieval law which now makes it a criminal offence to publish or utter a blasphemous comment. "It's very much part of a reform of our whole Constitution to make the country more modern". Exit polls and early results indicated the measure top remove was backed by over two-thirds of voters.
Mr Casey congratulated Mr Higgins following his victory, a described the presidential campaign as a "real experience".
His campaign was dogged by controversies over Aras spending, including his use of the Government jet.
The 37th Amendment has been officially approved by the people of Ireland.
Gavin Duffy joked that he was glad that times allotted for speeches were not in proportion to the number of votes gained.
Mr Gallagher is running for the presidency for a second time after a failed bid in 2011.
The MEP said she "looked forward to the conversation about a united Ireland being firmly on the agenda" in the coming seven years. "Really happy that you will continue to be our President for the next 7 years".
Sixteen years after achieving independence from Britain, the Republic of Ireland drew up a new constitution which included a clause on blasphemy. They were Sean T O'Kelly, Eamon de Valera, Patrick Hillery and Mary McAleese.
The result was largely expected, as the article on blasphemy in the constitution is generally agreed to be outdated and obsolete.