Thurmond was drafted 3rd overall by the San Francisco Warriors (now known as the Golden State Warriors) in the 1963 NBA draft. As a rookie, he mainly played a supporting role alongside Hall of Fame center Wilt Chamberlain. Thurmond averaged 7 points and 10.4 rebounds in his first NBA season and was named to the NBA All-Rookie Team in 1964.
After Chamberlain was traded to the Philadelphia 76ers during the next season, Thurmond blossomed into a highly productive starting center for the Warriors. Among his many accomplishments, Thurmond set a regular season record for rebounds in a quarter with 18, and averaged 21.3 and 22.0 rebounds per game in the 1966–67 and 1967–68 seasons. Thurmond placed second to Chamberlain in the MVP balloting in the 1966–67 season, averaged over 20 points per game each season from 1967–68 through 1971–72, and played in seven NBA All-Star Games as a member of the Warriors.
Thurmond also gained a fearsome defensive reputation in the NBA. Kareem Abdul-Jabbar called Thurmond the toughest defender he ever faced during his 20-season professional career. NBA All-Star center Bob Rule recalled Thurmond blocking six of his seven shots during the first half of their first encounter. After his coach urged him to "Keep putting ’em up. He can’t block ’em all," Rule responded "Yeah, well if I hadn’t made that layup it would have been all of ’em.”
However, even with the contributions of star teammates like Rick Barry, the Warriors were unable to win a championship with Thurmond at center. They reached the 1967 NBA Finals, but lost to Chamberlain's 76ers.
