A statement posted on her official Facebook page said: "Bonnie's family and team are heartbroken to announce that Bonnie unexpectedly passed away last night in hospital in Portugal as a result of the illness that she was being treated for."
"We will issue a further statement shortly, but for now ask for privacy to deal with this tragedy," the statement added.
Tyler had been battling serious health complications in recent months.
In May, her official Facebook page announced that she had undergone emergency intestinal surgery and had been placed in an induced coma.
An update issued on June 15 said she was no longer in a coma but remained "very unwell" and was receiving intensive care at a hospital in Portugal.
Born Gaynor Sullivan, Bonnie Tyler was a Welsh singer-songwriter celebrated for her distinctive husky voice and a career spanning nearly five decades.
She rose to international fame with her debut album The World Starts Tonight (1977), which featured the hit singles "Lost in France" and "More Than a Lover." Her 1977 smash hit "It's a Heartache" reached No. 4 on the UK Singles Chart and No. 3 on the US Billboard Hot 100.
Tyler achieved global superstardom in the 1980s after collaborating with songwriter and producer Jim Steinman, who wrote her signature hit "Total Eclipse of the Heart." Released as the lead single from her chart-topping 1983 album Faster Than the Speed of Night, the song sold more than 13 million copies worldwide and remains one of the best-selling singles of all time.
In 2003, she re-recorded "Total Eclipse of the Heart" with French singer Kareen Antonn. The bilingual duet, "Si demain... (Turn Around)," topped the French music charts.
Throughout her career, Tyler received three Grammy Award nominations and three Brit Award nominations, including two nods for British Female Solo Artist. In 2022, she was appointed a Member of the Order of the British Empire (MBE) in the Queen's Birthday Honours for services to music.
Tributes poured in following the announcement of her death.
Welsh First Minister Rhun ap Iorwerth expressed his condolences in a post on X, writing: "I am deeply saddened to hear of the passing of Bonnie Tyler."