[3] The first Catholics in the New Hampshire area were probably members of the Sokwaki and Pennacook tribes who had been converted by missionaries from the French colony of New France.

After New Hampshire became a British royal colony in 1680, it enacted discriminatory laws against Catholics, including the requirement of a Protestant oath for anyone seeking public office.

[4] During King William's War in the late 1600s, Native American allies of the French captured several women from the British settlements in the Province of New Hampshire.

[5] In 1694, during a French raid on British settlements near Durham, the first Catholic Masses in New Hampshire were celebrated by two Jesuit priests accompanying the expedition.

After the American Revolution ended in 1783, Pope Pius VI erected in 1784 the Prefecture Apostolic of the United States, encompassing the entire territory of the new nation.

[8] The first Catholic church in New Hampshire, St. Mary's, was built in 1823 in Claremont by a father and son, both Anglican priests, who had converted to Catholicism.

[4] At some point in the 1880s, Bradley contacted the Benedictine monks at Saint Mary's Abbey in Newark, New Jersey, about creating a Catholic college in New Hampshire.

He presided over a period of unprecedented growth in the diocese, founding 27 parishes in 11 years and authorizing the construction of nearly 50 churches and numerous schools, convents, and other facilities.

"[15] Pope John XXIII appointed Ernest Primeau from the Archdiocese of Chicago as bishop of Manchester in 1958 following Brady's death that year.

[17] In 1983, four nuns with the Sisters of Mercy settled a lawsuit against Gendron and the diocese after being fired from their teaching jobs in 1982 at Sacred Heart School in Hampton.

During his tenure, O'Neil worked to foster a common vision among New Hampshire Catholics with a program entitled "Renewing the Covenant."

In 2014, Edward Arsenault pleaded guilty to embezzling $300,000 during the 2000s from a Catholic hospital, the estate of a deceased priest and from McCormack.

In early 2002, Bishop McCormack announced the names of 14 diocesan priests who had been accused of sexually abusing children.

Court papers released in January 2003 showed that Bishop Gendron destroyed records of sexual abuse by two different priests during the 1980s.

A 2003 report by the Attorney General revealed that Gendron helped a priest accused of sexual abuse avoid criminal charges.

In 1975, police in Nashua, New Hampshire, had arrested Reverend Paul Aube, a diocese priest, after finding him with a boy in a car, both with their pants down.

[26] In July 2019, the diocese released a list of 73 priests and religious order members who were "credibly accused" of committing acts of sexual abuse.

[27] In July 2021, Bishop Libasci was named in a lawsuit accusing him of child molestation between 1983 and 1984 when he was parochial vicar at Saints Cyril and Methodius Parish School in New York.

The accuser, then 12 or 13 years old, said that Libasci fondled his genitals on "numerous occasions", including one instance when the boy was setting up the altar for mass.