Michael D Higgins was speaking at The Tim Parry Johnathan Ball Foundation for Peace in Warrington, Cheshire.
The centre is dedicated to the memory of the two boys killed in a terrorist bomb attack in the town in 1993.
Mr Higgins warned that radicalisation of young people is fast becoming one of the most significant global threats.
He said socially isolated people are increasingly invited to turn to extremism as they seek a purpose, a role and an identity.
"For all of us who are committed to the ideals of freedom, tolerance and peace, it is essential that we engage with those excluded individuals who may be drawn towards extremism and radicalisation," Mr Higgins said.
"We must give leadership in identifying and tackling the social conditions in which extremism can take root.
"Tackling issues such as youth unemployment, inadequate social infrastructure, and limited opportunity for participation are important in this regard, as is a critically-aware engagement with belief systems and ideologies, an engagement that eschews any imposition of claims of certainty, or fear or exclusion of 'the other'."
It is 22 years since three-year-old Johnathan Ball and 12-year-old Tim Parry died after the bomb detonated in a bin on Bridge Street in Warrington town centre.
No one has been charged in connection with the atrocity, which also left 56 people injured.
The Irish president has warned of the dangers of radicalisation during a visit to a peace centre founded in memory of two IRA bomb victims.