The news is a consolation for the franchise, coming nearly one month after Westbrook's fellow All-Star Kevin Durant left for the Golden State Warriors.
Terms of the contract were not announced, but multiple media reports said it was for three-years and $86 million.
"I am grateful to extend my contract with the Thunder and continue to play with the only organization that I have played for and have loved being a part of since I was drafted into the NBA," said Westbrook.
Westbrook recorded 18 triple-doubles last season, equalling the most in the NBA since Magic Johnson in the 1981-82 season.
He averaged 23.5 points, 10.4 assists, 7.8 rebounds and 2.04 steals last season.
Westbrook, 27, the fourth pick in the 2008 NBA draft, was due to become a free agent at the end of next season.
Westbrook and Durant turned the Thunder into contenders, leading the team to the Western Conference finals last season.
They held a 3-1 lead against Golden State before the Warriors won the final three games to clinch the best-of-seven series.
