The research has clear implications for promoting positive ageing and adult development, said lead researcher Patrick Hill of Carleton University in Canada.
"Our findings point to the fact that finding a direction for life, and setting overarching goals for what you want to achieve can help you actually live longer, regardless of when you find your purpose," said Hill.
"So the earlier someone comes to a direction for life, the earlier these protective effects may be able to occur," Hill said.
Previous studies have suggested that finding a purpose in life lowers risk of mortality above and beyond other factors that are known to predict longevity.
Hill and colleague Nicholas Turiano of the University of Rochester Medical Center took advantage of the nationally representative data available from the Midlife in the US (MIDUS) study.
The researchers looked at data from over 6000 participants, focusing on their self-reported purpose in life (eg, "Some people wander aimlessly through life, but I am not one of them") and other psychosocial variables that gauged their positive relations with others and their experience of positive and negative emotions.
Over the 14-year follow-up period represented in the MIDUS data, 569 of the participants had died (about 9 per cent of the sample). Those who had died had reported lower purpose in life and fewer positive relations than did survivors.
Greater purpose in life consistently predicted lower mortality risk across the lifespan, showing the same benefit for younger, middle-aged, and older participants across the follow-up period.
This consistency came as a surprise to the researchers.
"There are a lot of reasons to believe that being purposeful might help protect older adults more so than younger ones," said Hill.
"For instance, adults might need a sense of direction more, after they have left the workplace and lost that source for organising their daily events. In addition, older adults are more likely to face mortality risks than younger adults," said Hill.
"To show that purpose predicts longer lives for younger and older adults alike is pretty interesting, and underscores the power of the construct," he said.
Purpose had similar benefits for adults regardless of retirement status, a known mortality risk factor. And the longevity benefits of purpose in life held even after other indicators of psychological well-being, such as positive relations and positive emotions, were taken into account.
"These findings suggest that there's something unique about finding a purpose that seems to be leading to greater longevity," said Hill.
The study was published in the journal Psychological Science.