Don was born on August 2, 1944 in Port Arthur, Texas to Paul Gilmore Mahoney and Maureen Alma (Farmer) Mahoney. He moved to San Antonio, Texas with his parents and sister in 1949. As a child he loved playing with erector sets, and soon had designed and built motorized go-carts in which he would go "flying" down the street, to his Dad's consternation! Tinkering, designing, and building all came naturally to Don. However, some jobs were not that great, when he had to volunteer to fix his sister's car.

Don was a son, father, grandfather, mechanical designer, rancher, gun collector, could build and fix anything, and loved the Moody Blues, corvettes, trucks and cats. He was a member of the San Antonio Gear Grinders Car Club and in 1965 set a drag racing world record at the Greenvalley Raceway in his self-modified 1957 Chevrolet "Poor Red Trash".

He graduated from Jefferson High School in 1962 and received an Associate in Applied Science from San Antonio College in 1976. Don worked for the Texas Highway Department for five years as a draftsman and then joined Southwest Research Institute where he worked for 50 years beginning as a draftsman and retiring as a principal designer. While at SwRI, Clint Thwing and Don were awarded a patent for "Method and Apparatus to Propagate Crack Growth in a Workplace." He was also on a SwRI team that received the prestigious R&D 100 Award in 2019 for the "AF-369 VHF/UHF Terrestrial Direction-Finding Antenna". This award recognizes companies who have made significant innovations in research and development.

Don is survived by his son Michael, his grandchildren Christian, Megan, and Connor Mahoney, his sister Linda Louise Mahoney, and his long-time friend Diana Drenner. His parents preceded him in death.

A memorial service and reception were held at Porter Loring Funeral Home on March 8, 2022. Scattering of ashes will take place at the Mahoney Ranch at a later date. In lieu of flowers, memorials may be made to the San Antonio Leukemia And Lymphoma Society at LLS-South Texas, PO Box 735335, Dallas, TX 75373-5335.