A study of 3,800 people aged 52 to 79 found that those who rated their happiness the highest were significantly less likely to die in the following five years than those who were least content.
Even after taking into effect the impact of age, disease and lifestyle factors on people's happiness, researchers found that the happiest group had a 35 per cent lower risk of death than the least happy.
Although the results do not prove whether happiness actually causes longer life, they back up previous research which links wellbeing and a positive outlook to longer life.
Prof Andrew Steptoe, who led the study, said: "The happiness could be a marker of some other aspect of people's lives which is particularly important for health.
"For example, happiness is quite strongly linked to good social relationships, and maybe it is things like that that are accounting for the link between happiness and health."