Washington head coach Steve Sarkisian announced Polk's decision on Monday.
"Chris had a terrific career at Washington and deserves the opportunity to move on to the next level," Sarkisian said. "We wish him nothing but the best in what I'm sure will be a great professional career."
A first-team All-Pac 12 performer this past season, Polk rushed for 1,488 yards. He eclipsed the 1,000-yard mark in each of his last three years with the school.
In 40 career games at Washington Polk totaled 4,049 yards on the ground, just 57 yards shy of the school record held by Napoleon Kaufman.