The gene is responsible for keeping levels of cortisol – the stress hormone - under control.
"Suicide is a major preventable public health problem, but we have been stymied in our prevention efforts because we have no consistent way to predict those who are at increased risk of killing themselves," says study leader Dr Zachary Kaminsky, an assistant professor of psychiatry and behavioural sciences.
"With a test like ours, we may be able to stem suicide rates by identifying those people and intervening early enough to head off a catastrophe."
The blood test managed to predict those with the most severe risk of suicide with 90 per cent accuracy.
They could also spot if someone had already attempted suicide with 96 per cent accuracy, simply by looking at the levels of SKA2.
The SKA2 gene is found in the prefrontal cortex of the brain, and is involved in preventing negative thoughts and controlling impulsive behaviour.
If there isn't enough SKA2, or it is altered in some way, the body cannot control levels of cortisol. Previous research has shown that people who attempt suicide or who take their own lives have large amounts of cortisol in their systems.
A test could allow doctors or psychologists to place patients on ‘suicide watch’ and restrict their access to drugs or equipment which they could use to end their own life.
Dr Kaminsky said it could also help doctors know whether to give medications which are linked to suicidal thoughts.
"We have found a gene that we think could be really important for consistently identifying a range of behaviours from suicidal thoughts to attempts to completions," Kaminsky said.
"We need to study this in a larger sample but we believe that we might be able to monitor the blood to identify those at risk of suicide."
The research was reported in the American Journal of Psychology.