Expectant mothers who plan to breastfeed but are unable to are at the highest risk of developing the condition, experts found.
Around 13 per cent of new mothers experience post-partum depression within 14 weeks of giving birth.
They said that the effect that breastfeeding has on postnatal depression is not well understood and set out to investigate whether or not there is a link between the two.
The authors, from the UK and Spain, surveyed women who had almost 14,000 babies in the Bristol area during the 1990s when their children were two, eight, 21 and 32 months old.
They also examined whether or not the women suffered depression during their pregnancy.
Their study, published in the journal Maternal and Child Health, found that mothers who planned to breastfeed and who went on to breastfeed were around 50 per cent less likely to become depressed than mothers who had not planned to, and who did not, breastfeed.
Those who planned to breastfeed, but who did not go on to breastfeed were more than twice as likely to become depressed as mothers who had not planned to and did not, it found.
This link was found to be most pronounced when the babies were two months old but much smaller by the time they were eight months or older, they added.