Martin inked a one-year deal, NFL Network's Ian Rapoport reports.
Martin was released by the Tampa Bay Buccaneers on Feb. 20 after a disappointing 2017 season. He began the year finishing a suspension he drew in 2016 and returned to rush for 406 yards and just 2.9 yards per carry in 11 games.
He was first suspended at the close of the 2016 season for violating the league's policy on performance-enhancing drugs, reportedly by using Adderall. Martin entered rehab and said he returned "in a good place."
The Raiders were led in rushing last season by Marshawn Lynch, who finished the year with 891 yards and seven touchdowns.
Jon Gruden, who left the broadcast booth to return to the Raiders' sidelines, said he'd like to have Lynch back in the fold. It remains to be seen how Oakland's backfield will shape out.