McManus was ordained to the priesthood on May 27, 1978 by Bishop Kenneth Anthony Angell of Providence. He served as an associate pastor at several parishes and chaplaincies throughout the diocese for nearly twenty years. He was elevated to the title of Monsignor on February 28, 1997 by Pope John Paul II. McManus was consecrated as Auxiliary Bishop of the Diocese of Providence on February 22, 1999. On May 14, 2004, Bishop McManus succeeded Bishop Daniel P. Reilly as Bishop of the Diocese of Worcester, Massachusetts upon the latter's retirement. He was installed in Worcester on May 14, 2004. Bishop McManus criticized the College of the Holy Cross in Worcester for renting out "sacred space" to the Massachusetts Alliance on Teen Pregnancy for workshops. He expressed the view that the classes taught things which violated the teachings of the Catholic Church. On October 10, 2007, he issued a statement making known his criticisms of the conference.
Disputed property sale
In June 2012, on instructions from McManus, diocesan officials declined to sell a property owned by the diocese, an historic mansion in Northbridge, to a married gay couple. The property had been used as a Church-affiliated nonprofit retreat center. In September the couple filed suit against the bishop and other parties to the negotiations, citing an email in which church officials pulled out of the sale "because of the potentiality of gay marriages there." A lawyer for the diocese said that the Massachusetts anti-discrimination statute provides an exemption for religious institutions. He said: "If a religious entity did not have to permit property to be used for gay weddings, which we all agree, why must religious property be sold to an organization if it is going to be used for a gay wedding?" Massachusetts Attorney GeneralMartha Coakley filed a brief supporting the plaintiffs that said "we believe that this family was unfairly discriminated against by the diocese when it refused to sell them property based on their sexual orientation.... And no reasonable person would think that a wedding that took place on a property no longer owned by a church was endorsed by that church." Oral arguments in the case were scheduled in Worcester Superior Court on April 22, 2014.
Arrest
On May 4, 2013, McManus was arrested for drunken driving, leaving the scene of an accident, and refusing a chemical test in Narragansett, Rhode Island. After the alleged accident, the other person involved in the collision followed him and phoned the police. McManus was reportedly arrested about 20 minutes after the accident. He later stated: "I made a terrible error in judgment by driving after having consumed alcohol with dinner. There is no excuse for the mistake I made, only a commitment to make amends and accept the consequences of my action. More importantly, I ask forgiveness from the good people whom I serve, as well as my family and friends, in the Diocese of Worcester and the Diocese of Providence."
