An analysis of 299 nesting sites of all seven sea-turtle species found turtle-nest numbers had significantly increased at 95 sites, versus 35 that showed a significant decrease.
The study by an international team of scientists and published today in Science Advances, analysed data taken over an average of 16.2 years, including from waters off Australia, Africa, North and South America, and Asia.
They said the positive trends were likely linked to factors such as protection of eggs and nesting females as well as reduced bycatch.
Researchers say it is a welcome result that shows global conservation efforts can succeed, but they are treating the findings with "cautious optimism" and warn against complacency.
"People are putting a hell of a lot of effort into conserving turtles, and we want to show the efforts are working," study co-author Dr Gail Schofield said.
"But one of the biggest concerns with these positive stories is people might say, 'Well, why keep doing it now?'"
And there are other reasons the scientists urge caution.
Climate change impacts may not be detected for generations
Turtle numbers are estimated by counting the number of beach nests made by females at a specific site over a period of time and establishing an average.
This means any event that causes high juvenile mortality, as has been observed on Raine Island off the North Queensland coast, won't be reflected in population estimates until those turtles reach breeding age.
"We are seeing worrying trends [at Raine Island]," Dr Schofield said.
Rising sea levels resulting in beach erosion and collapsing nests at Raine Island — the world's largest green turtle hatching site — off the North Queensland coast has caused a dramatic drop in green turtle hatchling survival.
And at Mon Repos near Bundaberg, abnormally high sand temperatures in the 2016-17 hatching season killed more hatchlings than usual, as they became overheated on their way from nests to the ocean.
Australian marine park revision a 'huge shame'
The research comes as the Government is proposing changes to marine protection zones, established by the Gillard government in 2012, which would increase the area open to commercial longline fishing, game fishing and trawling.
Environment Minister Josh Frydenberg said in a statement in July the revised plans were "much more balanced" and allowed, "sustainable activities like commercial fishing while protecting key conservation features".
Public consultation for the review closed yesterday, with conservation bodies pressuring the Government to reconsider the changes.
Australian Marine Conservation Society (AMCS) spokesperson Adele Pedder described the revision as irresponsible.
"Marine parks give species such as turtles the best fighting chance," Ms Pedder said, adding that many species were endangered.
"While they're listed as endangered we're legally obliged to prevent and reduce mortality."
Dr Schofield also expressed concerns over the proposed changes.
"The protection zones are essential for providing protection not only for turtles but marine megafauna and other sea life," she said.
"It's just a shame to go backwards instead of forwards."