She shared images from the ceremony, reported to have been held on Sunday, on social media.
The couple met nearly a decade ago on the set of the film The Last Song.
In November, they lost their home in California in the state's devastating wildfires. The wedding is reported to have taken place at another property owned by Cyrus, in Franklin, Tennessee.
It was a small ceremony attended by family and close friends, reports said.
Pictures shared on Cyrus's Twitter account showed the couple embracing.
The couple became engaged in 2012 but then broke it off the following year and separated. They were seen together in 2015 and it was later announced that they were again engaged.
In November, Cyrus tweeted that she and Hemsworth had "made it out" safely as fire ravaged properties in Malibu.
But she also revealed that her house "no longer stands".
The singer recently overhauled the lyrics to Santa Baby, turning the Christmas classic into a feminist anthem.
She sang her version on The Tonight Show With Jimmy Fallon after pointing out that the lyrics ask Santa for "a car, a yacht and cheques" in exchange for a "hook up with Santa".
In her version, she said she doesn't need Santa's presents because she can buy her "own damn stuff".
She and musician Mark Ronson also released a version of John Lennon and Yoko Ono's Happy Christmas War is Over, recorded with the couple's son Sean Ono Lennon.
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