Mary Louise Mahon (Barnes), a devoted wife, mother, grandmother and devout Catholic was called home to the Lord Friday, October 16, 2026.

Born May 20, 1930 to Franklin and Catherine Barnes in the Bronx, Mary Lou was raised in Teaneck, NJ where she attended St. Cecilia High School. In high school, she was a cheerleader and was voted as the best actress in her senior class.

After high school, she graduated with an English degree from The College of Mount St. Vincent College in Riverdale, New York City. She used her English degree to land a job in advertising, first with McCann-Erickson then C.J. LaRoche.

Working at C.J. LaRoche changed her life. In 1956, her boss there set her up on a blind date with his friend Matt Mahon. They met for lunch at the Manhattan restaurant Kismet and then were married on June 1, 1957.

Her Catholic faith was the most important aspect of her life. After moving to Pittsburgh in the early ‘60s, she became very active at her parish Our Lady of Grace through the Christian Mothers and Women’s Guild. She was also one of the first women commissioned as a Eucharistic Minister at Our Lady of Grace.

After her faith, nothing mattered more than her family. She was married to Matt for nearly 70 years and they raised seven children.

Mary Lou is preceded in death by her sister Eleanor Kelly, brothers Frank Barnes, Richard Barnes and her daughter Bernadette Hale.

She is survived by her husband Matt, sisters-in-law Ruth Barnes and Elaine Barnes and her children: Matt (Theresa) Mahon, Kate (Robert) Truver, Emmet Mahon, Peggy Shorts, Gerard Mahon and Elizabeth (Tom) Pilarski. She was an adoring and devoted grandmother to 13 grandchildren and recently welcomed her first great-grandchild (Billy). Mary Lou was “Aunt Dooey” to 35 nieces and nephews.

Before and after raising her children, Mary Lou was an avid traveler. From multiple trips to Ireland, visiting Rome to see her brother Frank’s first Mass among other trips, she prioritized seeing the World. 

Outside of her faith and family, Mary Lou was an early member of People Concerned for the Unborn Child where she wrote and edited their monthly newsletter and served on its board for decades. She was also a founding member and served as president of the Pennsylvania Foundation for Life.

Mary Lou was also a board member at Angels’ Place Pittsburgh, which provides a holistic family development program for single, low-income full-time student parents and their children.

Family and friends welcome on Thursday, October 22, 2026 from 2:00 pm - 4:00 pm & 6:00 pm - 8:00 pm at WILLIAM SLATER II FUNERAL SERVICE (412-563-2800) 1660 Greentree Rd., Scott Twp. 15220. Mass of Christian Burial will be held on Friday, October 23, 2026 at 1:00 pm in St. Michael the Archangel Parish, Our Lady of Grace Church. 310 Kane Blvd., Pittsburgh, 15243. Burial to follow at The National Cemetery of the Alleghenies at 2:30 pm.

In lieu of flowers donations can be made to Catholic Charities or to the Capuchin Friars Provence of St Augustine. www.slaterfuneral.com