Theresa Margaret Carroll was born in New York City on August 28, 1943, to Charles Edward Carroll and Stephania Klapik Carroll. She was their only child. Charles died when Theresa was six years old and she was raised by her mother. She was educated through high school in Catholic schools graduating from Notre Dame High School near the top of her class.
Theresa attended Washington State College in Machias, Maine, until the end of her sophomore year when she transferred to the University of Maine at Orono. She graduated with a bachelor's degree in history and education in 1965, then attended graduate school for one semester.
She met and married Kenneth Edward Garnett in 1968 and settled near Ellsworth, Maine. They lived there for about 10 years. Their only child, David Edward, was born in 1973. During this time she joined Mensa. She worked for 10 years as a veterinary assistant in Ellsworth. She also bred German Shepherd dogs, Arabian horses, and operated a riding stable. She was active in local politics, although she never ran for office. At some point Theresa became interested in JFK assassination research. After studying the available information, she became an advocate for alternate explanations. She also, with her Mensa network, took part in demonstrations about injustices she encountered.
After a divorce, she and son David moved to Raleigh, North Carolina. In the Raleigh Mensa group, she met and subsequently married Robert Seay, an engineer at a local manufacturer of electronic components. She became a prominent member in this local Mensa group.
In 1988 Theresa and Robert moved to Asheville, North Carolina where she set up a consulting business. During the three years in Asheville, she wrote a number of articles and stories, some of which were published in various specialty magazines. She attended several conferences of JFK researchers and chaired one in Dallas on the 30th anniversary in 1993.
After moving to Connecticut, Theresa entered the graduate program at Western Connecticut University in Danbury in 1993. She finished the master's program there and was admitted to the University of Connecticut at Storrs for her doctoral studies. She was awarded her Ph.D. in History and Government in 2002. Her dissertation was about the discrepancies in the medical evidence between Parkland Hospital and the Bethesda autopsy of JFK.
After the 9-11 terrorist attacks, Theresa joined a local group of researchers where she put considerable effort into investigating and communicating with other colleagues. She continued this activity until her death on May 22, 2011.