Crennel, 62, was the Browns' head coach from 2005-08 and is committed to coaching in the East-West college all-star game in Orlando, Fla., Jan. 23.
He replaces Clancy Pendergast, who lasted just one season after the Chiefs ranked 30th out of 32 NFL teams, allowing nearly 390 yards per contest.
With the Chiefs, Crennel will be reunited with offensive coordinator Charlie Weis and General Manager Scott Pioli.
The latter trio worked together in New England and teamed to win three Super Bowl titles.
Weis, the former head coach at Notre Dame, became Kansas City's offensive coordinator last week. Piolo, New England's former personnel director, has been with the Chiefs one year.