The pope also accepted the resignation of Boston Auxiliary Bishop Emilio Allué, 75, from the office of auxiliary bishop.
Kennedy, 68, is the rector of St. John's, the main archdiocesan seminary, in Brighton.
Uglietto, 58, heads Blessed John XXIII, a national seminary located in Weston that has a student body made up primarily of older, second-career students.
As a result of the appointments, the archdiocese will have five active auxiliary bishops and three retired auxiliary bishops.
The auxiliary bishops assist Cardinal Sean P. O'Malley with the administration of the archdiocese, and have duties visiting parishes and celebrating confirmations.
O'Malley plans to introduce the new auxiliary bishops at a news conference in Braintree this morning, and then to celebrate Mass with them in the chapel at the archdiocesan headquarters.
SIC: BCom