Among the duties proper to the deacon is the proclamation of the gospel (See General Instruction for the Roman Missal 175,212); Introduction to the Lectionary for Mass 50; In the absence of a deacon, a priest may proclaim the gospel.
In the presence of a priest, deacon, or bishop it is not permitted for a lay person to proclaim the Gospel or indeed to fulfill any of the functions proper to their offices. This reflects the ancient tradition of the Church as expressed by the fathers of the Second Vatican Council.