[1] In 1883 she led a group of six other Sisters to the Kingdom of Hawaii to care for persons suffering leprosy on the island of Molokaʻi and aid in developing the medical infrastructure in Hawaiʻi.

The following year her family emigrated to the United States, settling in the industrial city of Utica, New York.

[6] By the time that their father died in 1862, the younger children in the family were of age to support themselves, so Barbara pursued her long-felt religious calling.

She helped found the first two Catholic hospitals in Central New York, with charters stipulating that medical care was to be provided to all, regardless of race or creed.

[9] In 1883, Mother Marianne Cope, by then Superior General of the congregation, received a plea for help from King Kalākaua of Hawaii to care for leprosy sufferers.

She responded enthusiastically to the letter: I am hungry for the work and I wish with all my heart to be one of the chosen Ones, whose privilege it will be, to sacrifice themselves for the salvation of the souls of the poor Islanders...

With Mother Marianne as a supervisor, the Sisters' task was to manage Kakaʻako Branch Hospital on Oʻahu, which served as a receiving station for Hansen's disease patients gathered from all over the islands.

She had to deal with a government-appointed administrator's maltreatment of the leprosy patients at the Branch Hospital at Kakaako, an area adjoining Honolulu.

Two years later, the king awarded Mother Marianne with the Cross of a Companion of the Royal Order of Kapiolani for her care of his people.

In November 1885, she opened the Kapiolani Home with the government's support to provide shelter to homeless female children of leprosy patients.

After the arrival of four Brothers of the Sacred Heart in 1895,[12] Mother Marianne withdrew the Sisters to the Bishop Home for leprous women and girls.

In 1993, Katherine Dehlia Mahoney was allegedly healed from multiple-organ failure after praying to Marianne Cope for intercession.

On December 20, 2004, after receiving the unanimous affirmation of the Congregation of the Causes of Saints, Pope John Paul II ordered a decree to be issued authenticating this recovery as a miracle to be attributed to the intercession of Cope.

At the Mass, presided over by Cardinal José Saraiva Martins, the Hawaiian song "Makalapua" (a favorite of Cope) was sung.

After the announcement by the Holy See of her impending beatification, during January 2005, Mother Marianne's remains were moved to the motherhouse of the congregation in Syracuse.

[25] In 2007, a statue of her was erected at St Joseph's Church in her native Utica, whose parish school she had attended as a child.

[27] On December 19, 2011, Pope Benedict signed and approved the promulgation of the decree for Marianne Cope's canonization, which took place on October 21, 2012;[28] a relic was carried to Honolulu from her mother church.

In 2014, the Church announced that Saint Marianne's remains would be re-interred at the Cathedral of Our Lady of Peace in Honolulu, a more convenient location for the faithful than the Kalaupapa National Historical Park on Molokaʻi, where access is primarily by plane or mule train.