John West owners to improve tuna fishing methods
Thai Union, which owns the John West tuna brand, said it will improve its fishing practices in the wake of a global campaign by Greenpeace.
It plans to reduce tuna fishing methods that harm wildlife and catch sharks, turtles and young fish accidentally.
The firm promised to make it easier to track where fish had come from and said it would improve working conditions.
Greenpeace said the moves by the world's largest tinned tuna company could encourage others to follow suit.
The environmental group's executive director Bunny McDiarmid said: "This marks huge progress for our oceans and marine life, and for the rights of people working in the seafood industry.
"If Thai Union implements these reforms, it will pressure other industry players to show the same level of ambition and drive much needed change. Now is the time for other companies to step up and show similar leadership."
Greenpeace and Thai Union will meet every six months to assess progress and at the end of 2018, an independent third party will look at the situation.
Thiraphong Chansiri, chief executive of Thai Union, said: "Thai Union has fully embraced its role as a leader for positive change as one of the largest seafood companies in the world.
"Thai Union looks forward to continuing to execute our SeaChange sustainability strategy, strengthened and enhanced by the joint agreement with Greenpeace and our shared vision for healthy seas now and for future generations."
The news comes two years after Greenpeace accused John West of continuing to use harmful "fish aggregation devices" to catch 98% of its tuna, despite a sustainability pledge to consumers.
Thai Union will also extend its ban on at-sea trans-shipping, unless suppliers meet strict conditions.
Trans-shipping involves catches being moved to other boats from fishing vessels, which then can stay at sea for months or even years at a time, raising the threat of human rights or labour abuses.