The disaster in April killed more than 1,000 textile workers and led to more than 80 brands who employ workers in Bangladesh to sign up to the union-backed Accord on Fire and Building Safety in Bangladesh.
River Island's signature follows an extensive push this month by unions and other campaigners for the retailer to change its position.
The move commits River Island to join with major brands and retailers in funding inspection and safety training in more than 1,700 factories across Bangladesh.
As a result of the accord, Bangladeshi workers will have the right to refuse to work in unsafe conditions and be entitled to full lay-off while any repairs, recommended by safety inspectors, are completed.
TUC general secretary Frances O'Grady said: "We're pleased River Island has stepped up its responsibilities for its workers' safety in Bangladesh.
"The few remaining brands outside the accord now need to consider their position more urgently."
River Island was one of eight UK retailers holding out against the Bangladesh fire and building safety accord, which has already been backed by most of the big names on the UK high street, including Zara, Next, Primark, New Look and Debenhams.
The spotlight now falls on the seven other UK-based brands, which are still refusing to sign the accord - Matalan, Bench Bank Fashion, Peacocks, Jane Norman, Republic and Mexx.
