But mental health has not been given the same public health priority as smoking, they said.
The study, published in the journal World Psychiatry, analysed previous research on mortality risk for a whole range of mental health problems.
The authors examined 20 papers looking at 1.7 million people and over 250,000 deaths.
They found that the average reduction in life expectancy for people with bipolar disorder was between nine and 20 years, it was 10 to 20 years for schizophrenia, between nine and 24 years for drug and alcohol abuse, and around seven to 11 years for recurrent depression.
The loss of years among heavy smokers was eight to 10 years.
"We found that many mental health diagnoses are associated with a drop in life expectancy as great as that associated with smoking 20 or more cigarettes a day," Dr Seena Fazel of the Department of Psychiatry at Oxford University said.
Dr John Williams, head of neuroscience and mental health at the Wellcome Trust, which funded the study, added: "This work emphasises how crucial it is that they have access to appropriate healthcare and advice
"We now have strong evidence that mental illness is just as threatening to life expectancy as other public health threats such as smoking."