The 36-year-old joins Paulo Sousa's side as a free agent after his contract at Serie A giants Inter expired.
Samuel enjoyed a trophy-laden nine-year stint at San Siro, collecting five league titles, three Coppa Italia medals and the UEFA Champions League in 2010.
Italian top-flight outfit Sampdoria had been linked with the Argentina international, but he has opted to make the move to Switzerland.
"I am very happy and look forward to the new challenge and the adventure of at Basel," Samuel told the club's official website.
Basel president, Bernhard Heusler, added: "With Walter Samuel Basel sign a very experienced player and also a great personality."
Samuel began his career with Newell's Old Boys in his native Argentina before switching to Boca Juniors.
Roma brought him to Italy in 2000 and his form in the Italian capital secured a move to Real Madrid four years later.
However, he would last just one year at the Santiago Bernabeu before returning to Serie A with Inter.
