Serena and Venus Williams told the U.S. Tennis Association they plan to play in the Fed Cup final against Italy in November.
Neither Williams has competed in the Fed Cup since 2007.
"You always want to have your best players," U.S. captain Mary Joe Fernandez said. "I am very excited that Venus and Serena have made themselves available."
The United States hasn't won a Fed Cup title since 2000, losing to Italy in last year's final.
The best-of-five match series is Nov. 6-7 on an indoor hard court at the San Diego Sports Arena.
Also on the U.S. roster are Melanie Oudin, Bethanie Mattek-Sands and Liezel Huber. Fernandez called it "one of the strongest lineups in years."
Serena Williams, who leads active women with 13 Grand Slam singles championships, is 7-0 in Fed Cup action, including 4-0 in singles. She last played for the U.S. in the 2007 quarterfinals.
Her older sister, who owns seven major singles titles, is 17-4 in the Fed Cup, 14-2 in singles. She last participated in the 2007 semifinals.