Heraldry speaks of two sides of a shield - dexter and sinister - which are right and left sides; these are reversed when viewed. The sinister, left side of the shield (right to the viewer), makes reference to the Archbishop's family and religious community: "Azure a Sun in its splendour Or charged with a monogram of the Holy Name Sable" (a golden sun inscribed with the first three Greek letters of the name of Jesus in black, all on a blue background). These, along with the motto, represent the bishop’s ties to the Society of Jesus or Jesuit Order. "Between a Shamrock slipped and a Rose in chief and a Fleur-de-lis in base all Argent" (on the upper level are a shamrock with stem attached and a rose, while on the lower level there is a lily - all these in silver). The shamrock and the rose represent the Archbishop's forebears in Ireland and England, and the fleur-de-lis his upbringing in Montreal, Quebec. The fleur-de-lis and the colour blue also represent the Blessed Virgin Mary, Mother of the Society of Jesus.
The right side of the shield (left to the viewer) blends the double-barred cross from the coat of arms of the Archdiocese of Halifax, chosen by Archbishop Prendergast during his episcopate there (the flowering cross, like the blazing sun represents the power of Christ's resurrection to transform human experiences into a share in Jesus glorification), with a new element the wavy blue Y-shape representing the three great rivers of the National Capital Region: the Ottawa, the Rideau and the Gatineau. The presence of the Cross above nature suggests the healing of Christ that touches not only people's lives but all of creation too.
The motto, "In nomine Jesu" ("at the name of Jesus") is taken from St. Paul's hymn to the crucified and risen Lord Jesus Christ in the Epistle to the Philippians (2:10). Besides expressing the desire that his ministry be in the name and manner of Jesus, it expresses its goal as the praise and glory of God, echoing the Jesuit motto Ad majorem Dei gloriam ("to the greater glory of God").
The achievement is completed by a reference to the pallium, a liturgical vestment (represented by the three black crosses on wool) conferred on metropolitan archbishops, by the Pope, who shares his universal jurisdiction with the Archbishop in the Ottawa ecclesiastical province, which includes the dioceses of Hearst, Pembroke and Timmins. The broad rimmed galero hat and the double-barred cross are also emblems of a metropolitan archbishop.