At the Vatican, after his Easter blessing, Pope Francis expressed his sadness by over the bombings in Sri Lanka.
"This is the one, non-negotiable certitude we have in life: His love does not change."
View photos of the service which included Liturgy of the Word, veneration of the cross, and Communion.
The Mass also recalls the institution of the priesthood at the Last Supper.
Twenty parishes will have new pastors.
Bishop Barres says he joins "in sorrow and prayer" with our Catholic brothers and sisters in Paris.
St. John Vianney, known as the Curé of Ars, is the patron saint of parish priests.