The rapper, whose real name is Dwayne Michael Carter, admitted possessing the .45 calibre gun and six rounds of ammunition after his private plane was searched on arriving in Miami from California on December 23, 2019.
A search warrant said the father-of-four told investigators the gun was a Father’s Day gift.
The 38-year-old entered the plea during a hearing held remotely before US District Judge Kathleen Williams.
“Your honour, I plead guilty to the charge,” Carter told the judge. He will be sentenced on 28 January.
The federal charge carries a maximum prison sentence of 10 years but it is likely Carter will get far less time than that. He is free on $250,000 bail but had to surrender his passport.
The charge stems from a weapons conviction for Carter in New York more than a decade ago, for which he was sentenced to eight months in prison.
Convicted felons are barred under federal law from possessing firearms.
Carter’s lawyer Howard Srebnick said he considered a motion to suppress the search of the plane as a violation of the rapper’s constitutional rights.
However, he said Carter wanted to accept responsibility.
“I must say I thought it was a very viable motion. He has decided not to pursue a motion to suppress,” Mr Srebnick said.
The Miami US attorney’s office also said in a news release that investigators found small amounts of cocaine, ecstasy and oxycodone in a bag belonging to Carter, but he was not charged with any drug crime.