For the killings of Maggie and Paul Murdaugh, 55-year-old Murdaugh is already serving two life terms.
In addition, he is serving a 27-year sentence for nearly two dozen state financial offenses, including money laundering and fraud.
Murdaugh acknowledged taking millions from client settlements and claimed to have used the money to support his drug addiction.
His current sentence, which is also for financial offenses, will run concurrently with his term in state jail. In addition, Murdaugh has to reimburse his victims for more than $8 million (£6.3 million).
The federal prosecutors recommended a sentence of 17.5 to nearly 22 years for the South Carolina-born Murdaugh. Murdaugh comes from a wealthy family.