Thomas Monson, who had headed the Mormon church since 2008, died at age 90 in the US state of Utah, the church announced.
"With tender feelings we announce that Thomas S. Monson, president and prophet of The Church of Jesus Christ of Latter-day Saints died... in his home in Salt Lake City," it said in a statement on Tuesday, using the church's official name.
"He died at age 90 from causes incident to age," it said.
President Donald Trump offered his condolences on Wednesday.
"While serving for over half a century in the leadership of his church, President Monson demonstrated wisdom, inspired leadership, and great compassion," Trump said in a statement.
"Considered a prophet by the nearly 16 million members of the LDS Church, his message was one of optimism, forgiveness, and faith," Trump said.
Monson became the 16th president of the Church of Jesus Christ of Latter-day Saints in February 2008 at age 80.
The Quorum of the Twelve Apostles -- who like the church's president are considered prophets by Mormons -- will select Monson's successor.
But the church said is this not expected to happen until after his funeral.
Founded in 1830 by American pioneer Joseph Smith, the Mormon church considers itself a Christian body, but bases its doctrines on the Book of Mormon, a text purporting to contain a fuller version of the words of Jesus Christ than that recorded in the Bible.
Smith said he received the content of the book on gold tablets during a vision of an angel called Moroni in 1827.
The Church of Jesus Christ of Latter-day Saints claims a total membership of more than 15.8 million people.