John Steven McCormack, 57, of Quincy, died peacefully, surrounded by the love of his family, on September 25, 2026. He was born January 15, 1969, to Barbara (Kelliher) Lynch McCormack and John P. McCormack. He was the cherished husband of Mary Elizabeth (Flater) McCormack and the loving and devoted father of Kate A. McCormack of Quincy, Steven T. McCormack of Brooklyn, NY, and Second Lieutenant Thomas G. McCormack, U.S. Marine Corps. He is also survived by Dorothy McCormack of Quincy, mother of his children. John was the dear brother of Gerard (Jaz) Lynch and his wife, Kathy; Kenneth Lynch and his wife, Denise; Elizabeth Lynch; Barbara Lynch and her husband, Charles Petri; and his sister-in-law, Mary Ellen Lynch. He was predeceased by his sister, Phyllis Munnis, and brother, Paul Lynch. He is also survived by many caring nieces, nephews, cousins, and their families.

John grew up the youngest of seven siblings in a large, close-knit Irish family in South Boston. He described his childhood as idyllic because of the love and support he knew then and throughout his life from his family and friends. He returned that love to others by being present, building relationships and giving of his time. John was a good, humble, and kind man who had a genuine joy for life. He was raised in the Catholic faith, which he nurtured and deepened throughout his life. His faith sustained him through many challenges, most especially during the past year as he battled glioblastoma. His family is deeply thankful for the expertise and compassionate care of his teams at Mass General Brigham Cancer Institute and Dana-Farber Cancer Institute.

John graduated from Don Bosco Technical High School and Wentworth Institute of Technology. He proudly served his country for five years in the United States Navy with Naval Mobile Construction Battalion 7, where he also formed lasting friendships and traveled extensively. After his military service, he worked for Maverick Corporation before beginning his 21-year career with the MBTA as a Senior Project Manager in the Capital Delivery Department. Most recently, he served as president of the MBTA Management Union, United Steel Workers, Local #9501.

John raised his family in Quincy and was always involved in the education and activities of his children. He was a dad who was present, cheering from the sidelines and celebrating his children’s successes. John had a builder’s spirit and lifelong curiosity with passions for hiking, running, sailing, Boston sports, volunteering, and continuous learning. He especially loved cycling, often setting out on long distance rides of more than 100 miles and participating in the Best Buddies Challenge. May he rest in the perfect peace of our Father in Heaven.

Visiting hours will be held at Keohane Funeral Home, 785 Hancock Street in Quincy, on Monday, October 5, from 3–7 p.m. A Funeral Mass will be celebrated at St. John the Baptist Church, 44 School Street, Quincy, on Tuesday, October 6, at 10 a.m. Interment will follow at the Massachusetts National Cemetery in Bourne, MA.

For those who wish, donations in lieu of flowers may be made to Glioblastoma Research Organization at Gbmresearch.org.