McMullen was born as Catherine C. Kennedy in Gulph Mills, Pennsylvania on 30 August 1912. She graduated from Gordon High School in Coatesville, Pennsylvania in 1930. On 17 June 1932, aged 19, she married J. Hubert “Hubie” McMullen, with whom she had two sons, James and J. Michael.

After renting properties for several years, the couple built their own house in 1951, where McMullen lived for the rest of her life. She worked at the Department of Welfare, Collins and Aikman Corporation, and later at Pepperidge Farm, where she worked with sales statistics. She was widowed in 1968 and retired from the farm in 1977.

In her later years, McMullen volunteered for Meals on Wheels. She was active in her community, being members of organisations including the Order of the Amaranth and Trinity Lutheran Church, where her late husband had been the choir director. She also joined Caln Privileged Citizens, an over-60s club in Caln Township.

At the time of her 105th birthday, McMullen had five grandchildren and eight great-grandchildren, as well as her two sons. She enjoyed cooking and playing bridge as a centenarian. She died on 27 March 2023 at the age of 110 years, 209 days.