The couple tied the knot in September 2017 and have a two-year-old daughter, Kulture.
Court records show Grammy-winning hip-hop star Cardi B, whose real name is Belcalis Almanzar, filed for divorce in Georgia on Tuesday.
The couple are living in a "bona fide state of separation," court documents state, and the marriage is "irretrievably broken".
And there are "no prospects for a reconciliation," the papers say.
Cardi B, 27, is asking for "primary physical custody" of Kulture and requests Offset, whose real name is Kiari Cephus, contributes to the child's "support and maintenance".
The now former couple have their marital home in Fulton County, Georgia, the legal papers state.
Cardi B and Offset married in secret, not revealing the news until a year after they walked down the aisle.
Their relationship appeared to be on the rocks amid rumours of his cheating and Offset took to the stage at Cardi B's Rolling Loud concert in 2018 to ask for forgiveness.
Offset, 28, is best known for performing with the chart-topping rap group Migos.
Cardi B is asking for the couple's assets to be split evenly.
The Bronx-born star has enjoyed a meteoric rise in recent years, going from cast member on reality TV series Love & Hip Hop: New York to one of the biggest artists in music.
She released her debut album, Invasion Of Privacy, in April 2018 and backed by the singles Bodak Yellow, I Like It and Be Careful topped the charts in the US.
The latter song is reportedly about Offset's alleged infidelity. Invasion Of Privacy won best rap album at the Grammys and was also nominated for album of the year.
In a February 2018 interview with Cosmopolitan, Cardi B explained why she did not leave Offset following allegations he had cheated.
"It's like everybody is coming down my neck like, 'Why are you not leaving him? You have low self-esteem'," she told the magazine.
"But that couldn't be farther from the truth. I don't have low self-esteem. I know I look good. I know I'm rich, I know I'm talented. I know I could get any man I want - any basketball player, football player."
However, the rapper said she wanted to work on her relationship with Offset, saying what he did was "not right" but "I ain't no angel".
Her latest single, WAP, the explicit duet with Megan Thee Stallion, hit number one in both the US and UK following its release in August.