Researchers said the findings were of 'crucial importance' because they could provide a simple way for GPs to identify patients at increased risk of premature death.
The research, published in the journal BMC Medicine, shows that patients with long-term conditions - particularly where mental health conditions are involved - are at a higher risk of missing appointments than patients with no long-term conditions. Where patients miss two or more visits to the GP within a year, their risk of death rises sharply.
Compared with patients who do not miss an appointment, risk of death is three times higher among patients with 'physical health-related long-term conditions alone' who miss two appointments or more, the research shows.
For patients with 'only mental health related long-term conditions' who miss two appointments or more, all-cause mortality is eight times higher compared with patients who do not miss appointments.
GPonline revealed last month that more than 16m GP appointments are missed each year in England in total. Previous research has shown that more than half of GP appointments are for patients with multimorbidity - suggesting that millions of patients at increased risk of premature could be tracked through missed appointment data.
Patients with multiple long-term conditions were significantly more likely to miss GP appointments than patients with no long-term conditions, the team from the University of Glasgow and colleagues from Lancaster University and the University of Aberdeen found.
Nearly half of appointments missed - 46% - were for patients with one or two long-term conditions, the study found. Patients with four or more conditions accounted for 17% of missed appointments - and patients in this group were 'more than twice as likely to miss appointments' as those with no long-term conditions, even after controlling for other factors that affect attendance.
Professor Philip Wilson, a researcher involved in the study, said: 'These findings are crucially important for GPs wishing to identify patients at high risk of premature death. For people with physical conditions missed appointments are a strong independent risk factor for dying in the near future.
'Among those without long-term physical conditions, the absolute risk is lower, but missing appointments is an even stronger risk marker for premature death from non-natural causes.'
RCGP chair Professor Helen Stokes-Lampard said: 'Patients with long-term conditions need regular monitoring and treatment and advice tailored to their unique health needs, so missing appointments and not being able to access that support has the potential to have a devastating impact on their wellbeing.
'People miss appointments for a range of reasons, but this study highlights why it’s more important to show compassion to people who fail to attend, rather than punishing them - for some, life gets in the way and they forget, but others might not turn up precisely because of their health issue.
'As this research has demonstrated, this particularly applies to patients with mental health conditions. GPs try to be extremely sensitive to this and will attempt to chase up those they are particularly concerned about, but some patients will be living with a mental health issue that the GP is not aware of and so the risk heightens.
'We need systems in place to better accommodate for these situations and the starting point is having more mental health therapists based in primary care, where the majority of mental health issues are identified and managed.'