Mary was baptized on 27 Feb 1807 in Lusk, Dublin (birth date is approximated). She married Thomas Kelly on 26 Apr 1827 at St Andrew's RC Church in Bagenalstown (aka Muine Bheag), Newtown townland (Agha civil parish), County Carlow.

Thomas & Mary (with their 9 children) emigrated from their home in the tiny hamlet of Newtown, Carlow to Canada in 1847. It was the time of the Great Famine in Ireland (1845-1849), with mass starvation and tenants unable to pay rent to land owners. With ship voyages lasting up to 3 months, cholera and typhus easily spread in the cramped and unsanitary conditions, leading to death rates of 20-50%, and earning them the name of 'coffin ships'. Thomas & Mary lost 3 children during the voyage; two have been revealed, a son named James (less than 1 year old), and another named Peter (abt 3 years old). However, the 3rd child remains unknown, though it appears he/she was also very young. Their story was often repeated by their sister Elizabeth [Kelly] Carter to her children; one of her grandchildren (Carmel (Burns) James) later wrote "Elizabeth told Mama that many of her fellow passengers, including some members of her own family, died of cholera and typhus on board the ship. Sandbags were tied to the bodies of the dead persons and they were dropped overboard. The reason for the sandbags was to ensure that the bodies would sink rapidly to the bottom of the ocean so that sharks would not have a chance to eat them. Elizabeth's mother would often cry for the loss of her three children."

Shortly after arriving in Canada, Thomas obtained a government grant for 60 acres of land in Huntley Twp, Ontario, a property now known as 649 Upper Dwyer Hill Road, Ottawa, Ontario. The family built a log house there, and it still exists today (see photo, taken 2011); the last inhabitants were Thomas & Mary's granddaughter Mary Anne Kelly and her husband Patrick Mantil (m. 1922). Since then it has been used as a shed, with a new home built at the back of the property. A 3g-grandson of Thomas & Mary still owns the property and lives there with his family (as of 2022).

The family attended St. Michael's RC Church in Corkery, and some of their descendants still attend to this day. Thomas and all but one of their children were buried in the church cemetery, located directly across the road (St Michael's RC Cemetery). Mary died some time between the 1871-1881 Censuses of Canada, but no death or burial record has yet been found for her. Regardless, there is little question she was buried with her family.

No visible gravemarker has been found for Thomas (or Mary) at St Michael's RC Cemetery. However, their 3g-grandson who still owns their original property was also the volunteer caretaker of the cemetery. He reported that many of the earliest graves were dug up and moved to other areas of the cemetery long ago, when a 'road' was needed within the cemetery (likely after the cemetery vault was built, so horse & wagon could access it without riding over graves). It's possible Thomas & Mary's graves were among those that were moved. [H. Presley, 3g-grandson]