The research, involving 790 American men, was led by the University of Pennsylvania in partnership with 12 other research facilities.
The scientists looked into how testosterone therapy could benefit men in three main areas: sexual function, physical function and vitality.
During the study, men over the age of 65 were either prescribed testosterone therapy or given placebo pills.
The researchers found that men who received the testosterone treatment for one year experienced "significant improvements" in sexual function.
Most notably, their sexual desire and erectile function improved when compared to men who had been taking the placebo tablet.
Study co-author Professor Thomas Gill, of Yale School of Medicine, said in a statement: "There appears to be benefits for treatment with testosterone among men who have unequivocally low levels of testosterone that are attributable solely to age.
"The benefits were quite convincing for sexual function."
The participants also underwent tests to monitor differences in physical function after taking the testosterone tablets.
When walking speed of the men was monitored, the researchers noticed a slight improvement in the HRT group compared to the placebo group - the former could walk 50 metres further in six minutes than the latter.
Finally, participant's moods were monitored and the scientists noted that men receiving HRT experienced "improved mood and fewer depressive symptoms" when compared to the placebo group.
Professor Gill concluded: "We found that testosterone improved men's impression that their sexual desire, walking ability, energy level, and overall health were better."
However, the researchers did acknowledge that more research is needed into the long-term health implications of men taking testosterone medication.
Commenting in the New England Journal of Medicine, Dr Eric Orwoll added: "It is a landmark study in the field of men's health and no doubt a bell-wether [trend setter] for additional important contributions.
"Their report is important, not only because it deals with an essential public health issue but also because the investigators have succeeded in conducting the kind of well-conceived studies that are sorely needed."