Mercedes was born May 30, 1898, the oldest child of John and Elizabeth Greenwell Thomas in Morganfield, Ky. She was 6 years old when her mother died. Aunt Minnie Thomas took Mercedes to make a home for her with the six children of her own. Mercedes spent her first school days at St. Vincent Academy in St. Vincent. She later came to Mount Saint Joseph Academy. In 1913, she responded to the call to religious life and entered the novitiate at Mount Saint Joseph. After a few weeks of postulancy, Mercedes received the Ursuline habit and the name Sister Mary Benedict on August 5, 1913.
Sister Mary Benedict began her mission work by keeping house at Holy Cross in Loretto, Ky. Living conditions were primitive but she prepared the meals, did the laundry, and kept the convent spotless. In 1920, she was assigned to classroom teaching. She was missioned to teach primary grades at Clementsville, Knottsville, Calvary, Howardstown, and Fredericktown in Kentucky; in Wynot and Plattsmouth, Neb.; and in Wilhelmina, Mo. Missioned back to Kentucky, she taught at Raywick, Stanley, Leitchfield, Cloverport, St. Francis, and Owensboro (Precious Blood and Immaculate). In 1965, she was assigned to teach fourth grade at St. Bartholomew School in Buechel, Ky. When Sister Mary Benedict did not appear in the chapel for morning meditation and office on May 18, 1965, the Sister who went to her room found her fully dressed, sitting in her armchair. She had died of a heart attack.
That same evening, a wake service was held at St. Bartholomew Church. The next morning, Father Bartholomew Beruatto, pastor, and Father Henry Mitchell concelebrated a Mass for the Dead. Following the Mass, Sister’s remains were brought to Mount Saint Joseph. On May 21, the funeral Mass was celebrated by Msgr. Albert Thompson, chaplain, and Msgr. Edward Russell. Sister Mary Benedict’s remains are buried in the convent cemetery.