He is the author of the Mitochondrial Free Radical Theory of Aging. He is now working to develop a tissue-repair strategy that would rejuvenate the human body and thereby allow an indefinite lifespan -- a medical goal he calls engineered negligible senescence. To this end, he has identified seven tissue-damages caused by aging that need to be repaired medically before this can be done.
De Grey argues that the fundamental knowledge needed to develop effective anti-aging medicine mostly already exists, and that the science is ahead of the funding. He works to identify and promote specific technological approaches to the reversal of various aspects of aging, or as de Grey puts it, "the set of accumulated side effects from metabolism that eventually kills us,"[5] and for the more proactive and urgent approaches to extending the healthy human lifespan. Regarding this issue, de Grey is a supporter of life extension.
As of 2005, de Grey's work centered upon a detailed plan called Strategies for Engineered Negligible Senescence (SENS) which is aimed at preventing age-related physical and cognitive decline. He is also the co-founder (with David Gobel) and chief scientist of the Methuselah Foundation, a 501(c)(3) nonprofit organization based in Springfield, Virginia, United States.
A major activity of the Methuselah Foundation is the Methuselah Mouse Prize, a prize designed to hasten the research into effective life extension interventions by awarding monetary prizes to researchers who stretch the lifespan of mice to unprecedented lengths. Regarding this, de Grey stated in March 2005 "if we are to bring about real regenerative therapies that will benefit not just future generations, but those of us who are alive today, we must encourage scientists to work on the problem of aging." The prize reached US$4.2 million in February 2007. De Grey believes that once dramatic life extension of already middle-aged mice has been achieved, a large amount of funding will be diverted to this kind of research, which would accelerate progress in doing the same for humans.