The deal Tuesday came after James was released Sept. 8 by the San Francisco 49ers, who took him in the second round of the 2012 draft.
The Dolphins have five other running backs under contract, including Knowshon Moreno, who has missed the past two games because of an elbow injury.
James was frustrated by his lack of playing time with the 49ers and has 41 career carries while averaging 4.5 yards per attempt. He was used mostly on returns, averaging 10.9 yards on punt returns and 28.4 on kickoffs.
James finished third in Heisman Trophy voting in 2010 and 10th in 2011 at Oregon.
AP NFL website: www.pro32.ap.org and http://twitter.com/AP-NFL