Mary Whereat was born aboard the Matilda Atheling on April 11, 1874. Her father, William Joseph Whereat, was the ship's captain and her mother, Ellen Elizabeth Oxley Whereat, had accompanied him on the voyage. Her two older brothers, Lancelot Arthur Whereat and Alfred Ernest Whereat, were also on board. At the time of Mary's birth, the ship was located in the Indian Ocean, outside the Sunda Strait between Java and Sumatra. Her parents were British citizens and members of the Church of England, and when the ship reached Melbourne, Australia, she was baptized at the Holy Trinity Church under the name Ellen Mary Whereat. She returned to England in May of 1875 after spending the first year of her life at sea.
Mary was raised by her mother at their home in Bristol while her father was frequently absent at sea. William Whereat maintained contact with the family through weekly letters. When Mary was nine years old, her father accepted a position training seamen for the Royal Naval Reserve. This necessitated a move to Forest Gate, Essex, where Mary was enrolled at the Ursuline Convent School. The school provided Mary with an introduction to Catholicism. She began attending catechism classes at her father's request. When Mary's mother died in 1890, she became a boarder at the Convent. Her father converted to Catholicism later that year. Mary made her profession of faith on June 28, 1891.
In October of 1891, Mary left England with her father to live with her brother Lance and her uncle Robert Barnett in Oregon. They set sail on October 31 aboard the S.S. Dominion for Montreal with a stop in Quebec to visit the Ursuline Convent. From Montreal, they traveled by the Canadian Pacific Railway to British Columbia, where they boarded a boat for Tacoma, Washington. They then traveled by train to Oswego, Oregon, where they arrived on November 31.
Mary enrolled in school at St. Mary's Academy in Portland. She remained there for two years as a member of Sister Mary Flavia's advanced class. With her father's encouragement, she entered the novitiate of the Sisters of the Holy Names of Jesus and Mary on November 1, 1892. She received the name Sister Mary Ursula and made her first vows in 1894. She made her final vows in 1899. Sister Mary Ursula taught high school throughout much of her career. She taught at St. Rose Academy in Seattle, Sacred Heart in Salem, St. Mary's in The Dalles, Holy Names Academy in East Portland, St. Mary's in Medford, and St. Mary's in Portland.
Sister Mary Ursula passed away on May 5, 1963 in Lake Oswego and was interred in the Marylhurst Convent Cemetery.