The findings, published in leading general medical journal The Lancet, should be a useful guide to doctors weighing options for treating flu, the authors said.
The research collated data from 78 studies, covering more than 29,000 patients in 38 different countries, admitted to hospital during the H1N1 flu scare.
A novel flu strain, H1N1 initially stoked fears of a massive death toll in line with flu pandemics of the previous century.
But the strain turned out to be far less lethal, with a mortality rate similar to that of annual, or "seasonal", strains of flu.
Tamiflu -- lab name oseltamivir -- is the most widely used of two frontline drugs used to fight flu by inhibiting viral replication.
The study found that people older than 16 who were given Tamiflu in hospital had a 25 percent lower risk of death than those who did not get the drug.
Among a sub-group of those who received Tamiflu swiftly, within the first two days of admission, the mortality risk was halved, and among pregnant woman it was reduced by 54 percent.
There was no significant impact on risk among children given the drug.
The study, carried out by independent epidemiologists, was financed by Tamiflu's makers, Hoffmann-La Roche.
The Lancet is a peer-reviewed journal, meaning that papers are vetted by external experts before publication.