President Michael D Higgins laid a wreath at the monument at the Church Square for the seven people who lost their lives in the bombing five decades ago.
Hundreds of people gathered just meters from where a no-warning car bomb exploded on the evening of the 17th May 1974.
Church bells rang out across the town, marking the precise time of the blast at 6.58pm. 34 people lost their lives that day including an unborn baby. Up on 300 others were injured over the course of the bombs that exploded in Monaghan and Dublin.
President Michael D. Higgins met with families of the victims and survivors in Monaghan and he reiterated his calls that the victim's families deserve answers.