Mansell was ordained to the priesthood in Rome for the Archdiocese of New York by Archbishop Martin O'Connor on December 19, 1962.

He received his episcopal consecration on January 6, 1993,[4] from the pope, with Archbishops Giovanni Re and Justin Rigali serving as co-consecrators, in Rome.

In September 2003, New York Governor George Pataki named Mansell to the State Commission on Education Reform.

In 2006, Buffalo Business First reported that Mansell's successor, Bishop Edward Kmiec, said that some statistics were too optimistic, and that the diocese would have to close some parishes and schools to address declining attendance and enrollment, as well as a $3 million diocesan debt.

In 2005, the archdiocese paid $22 million to settle sexual abuse claims brought by 43 people against 14 priests, the majority of cases occurring in the 1960s and 1970s.

[9] Mansell was quoted in a New York Times article stating: "[It is] part of a healing process for the persons whose lives have been severely harmed by the evil of sexual abuse and for the Church itself.

[10] Having reached the mandatory retirement age of 75, Mansell submitted his letter of resignation as archbishop of Hartford to Pope Francis.