According to the Catholic Church's Canon Law, the following outlines who may proclaim the Gospel and give the homily at Mass:
Proclaiming the Gospel:
* Deacons: Deacons are the ordinary ministers of the Gospel at Mass. This is a specific role assigned to them by ordination.
* Priests: Priests (and Bishops) can also proclaim the Gospel.
Giving the Homily:
The Code of Canon Law (Canon 767 §1) is very specific on this point:
* Priests and Deacons: "Among the forms of preaching, the homily, which is part of the liturgy itself and is reserved to a priest or deacon, is preeminent..."
Therefore, the homily is reserved to priests and deacons. No one else is permitted to give the homily during Mass.
Important Considerations:
* Lay People and Testimonies: Lay people can give testimonies or reflections *outside* of the homily during Mass. For example, before or after Mass, or during special prayer services. The USCCB clarifies that "other members of the faithful may offer reflections on the Scriptures outside of the Mass," or even "offer witness talks within the Mass, but these cannot be homilies and should not occur at the time when the homily is to be given"
* Extraordinary Circumstances: While exceedingly rare, in very specific and serious circumstances (such as the absence of a priest or deacon and a grave spiritual need), a bishop might grant special permission for a lay person to preach, but this is NOT during the Mass. The homily during Mass remains reserved to ordained clergy.
In summary: Deacons and Priests can proclaim the Gospel and preach the homily during Mass. No one else can preach the homily during Mass.