Three pairs of Lord Howe Island stick insects have reached adulthood and laid eggs after they themselves hatched from eggs brought from Melbourne Zoo.
The critically endangered creature was thought to be extinct for almost 80 years until its rediscovery in 2001.
Only about 20-30 individuals are left in the wild.
Mark Bushell, curator of invertebrates at Bristol Zoo, said he was "ecstatic".
"To have the opportunity to work with this critically endangered species is a dream come true for me, and now to have bred them is a career highlight.
"This species is very difficult to keep, so to have six individuals reach adulthood is an incredible success for the global conservation programme for this species, to help bring them back from the brink of extinction."
A batch of 300 eggs was sent to Bristol from Melbourne last November as part of an international effort to save the species.
Other eggs were sent to zoos in Toronto and San Diego, with the aim of eventually returning the species to Lord Howe island.
One of the world's rarest stick insects has successfully bred at Bristol Zoo - the first time the species has done so outside Australia.