In 1975, she was appointed Professor of Criminal Law, Criminology and Penology at Trinity College Dublin, and in 1987 she returned to her alma mater, Queen's, to become director of the Institute of Professional Legal Studies.

These steps included celebrating the Twelfth of July at Áras an Uachtaráin and taking Communion in a Church of Ireland cathedral in Dublin, for which she incurred some criticism from some of the Irish Catholic hierarchy.

[33][34] In 1975, having spent a year as a practising barrister in Belfast, she was appointed Reid Professor of Criminal Law, Criminology and Penology in Trinity College Dublin,[35] succeeding Mary Robinson.

McAleese was the author and presenter of a successful BBC Radio Ulster series called "The Protestant Mind" which encouraged the divided communities in Northern Ireland to try to stand in each other's shoes.

[39] In 1997, McAleese defeated former Taoiseach Albert Reynolds and former minister Michael O'Kennedy in an internal party election held to determine the Fianna Fáil nomination for the Irish presidency.

While Cardinal Desmond Connell called her action a "sham" and a "deception", Taoiseach Bertie Ahern said it was ironic that "the Church was condemning an act of reconciliation and bridge-building between the denominations".

Following the failure of any other candidate to secure the necessary support for nomination, the incumbent president stood unopposed, with no political party affiliation,[43] and was declared elected on 1 October 2004.

McAleese's very high approval ratings were widely seen as the reason for her re-election, with no opposition party willing to bear the cost (financial or political) of competing in an election that would prove difficult to win.

[50] She was accompanied by her husband, Martin, Cardinal Desmond Connell, Mary Hanafin, the Minister for Education and Science, together with bishops and other pilgrims.

[63][64] She spoke kindly of Mikhail Gorbachev, officially invited Medvedev to Ireland, and addressed students at a university in Saint Petersburg.

[65][66][67] On her state tour to Russia, highlighting the importance of competence, she launched an unprecedented attack on the Central Bank of Ireland, for their role in the financial crisis which resulted in tens of thousands of people in mortgage arrears.

[70] In March 2011, President McAleese invited Queen Elizabeth II of the United Kingdom to make a state visit to Ireland.

[75] While opening the National Ploughing Championships in County Kildare in September 2011, she spoke of her sadness that she would soon no longer be president, saying: "I'm going to miss it terribly ...

[84] She performed her last official public engagement at a hostel for homeless men in Dublin in the morning and spent the afternoon moving out of Áras an Uachtaráin.

[17][88] She had previously said that she obtained a master's degree and licentiate in canon law and her interest grew because of her concern about what has been happening in the Church – the sexual abuse scandal, among other things.

On 22 September 2018, McAleese publicly defended her thesis on "Children's Rights and Obligations in Canon Law" at the Pontifical Gregorian University.

"[106] In response to her speech, the Archbishop of Dublin Diarmuid Martin said "Her challenge to the internal culture of the Church today was brutally stark.

[108] Irish born Cardinal Kevin Farrell and Prefect of the Dicastery for Laity, Family and Life banned McAleese from speaking in the Vatican.

Acknowledging that the Synod will doubtless be considering the Catholic Church's pastoral approach to homosexuals, McAleese described herself as "cynical" about the outcome of the forthcoming three-week consultation.

[114] On 23 August 2019, McAleese was announced as the winner of the Alfons Auer Ethics Award, from Tübingen University in Germany for her political dedication in building bridges across divisions in society, especially in the conflict in Northern Ireland, her commitment to reforming the Catholic Church after the sexual abuse scandals, her theological and ethical advocacy for the rights of children, for the complete equality of women in church ministries and for the acceptance of diversity.

In her address McAleese called for "a clear acknowledgement from the Catholic Church that the canon laws which constrict children's rights have now been overtaken by the (UN) Convention and our Constitution"[117] McAleese has written to Pope Francis threatening to quit the Catholic Church if it comes to light the Vatican "failed to act to protect members of the L'Arche community" from the organization's founder Jean Vanier.

[118] McAleese strongly promoted closer ties between Ireland and the People's Republic of China,[119] meeting frequently with officials from that country's ruling Chinese Communist Party, including Xi Jinping and former President Hu Jintao.

[121] According to the Sunday Independent, Chinese universities "provided the fourth highest amount of non-EU collaborations with Trinity over the previous 10 years, with 581 co-publications."

She said "The toxic attitudes which were heard in homes, streets, workplaces even in schools and churches caused untold suffering and nothing is surer than the fact that those attitudes can have and will have no place in the Ireland we are building, for they belong in the same toxic waste dump along with sexism, racism, sectarianism and all those other contrary forces which would diminish the innate dignity, freedom and nature of the human person, reduce their life chances and opportunities and consign them to half-lived lives.

McAleese said she met the Apostolic Nuncio, Archbishop Charles John Brown, shortly after Easter to raise with him her concern about the growing number of suicides among young men in Ireland.

[130] In 2016, McAleese received The Northern Ireland Tolerantia Award for "her commitment to equal treatment and the dignity of LGB&T people for over four decades".

McAleese warned that Britain's departure could result in the return of border controls on the island of Ireland and cause a "potential drift" in the peace process.

McAleese said "the lawyer in me says our migration controls are very different, and they are going to be if Britain is no longer part of the EU, and if they tighten the migration controls it won't be enough that I'm entitled to use the Common Travel Area...how are they going to differentiate between me, the person who is entitled to plead the Common Travel Areas, and the person say from France or Germany or Poland who's going to cross the road at Newry, or Derry?

She said "The process of Brexit has been like watching a political form of necrotising fasciitis as it has devoured time, effort, goodwill, patience, reputations, relationships, engendering huge volumes of work, of anxiety and again, no obvious end in sight.

I harboured a hope that somehow, the United Kingdom would step back from the brink and recommit to the ideal of the European Union, in my view the greatest and the noblest political undertaking ever envisaged and realised in human history.