Terms of the deal were not disclosed.
Rainey, out of the University of Florida and high school teammate and friend of Steelers C Maurkice Pouncey, will add another element of competition to a position shaping up to be the fiercest training camp battle.
With incumbent Rashard Mendenhall tearing his ACL
in the playoffs in Week 17 (I beg for your forgiveness) the Steelers go into OTAs and training camp likely with Isaac Redman as the feature back, and Jonathan Dwyer, John Clay and Baron Batch joining Rainey for what will probably be two other game-day spots.
A diminutive but lightning fast multi-purpose running back, Rainey has good pass catching skills and will likely vie for the 53-man roster as a return man as well as a versatile offensive threat.
Rainey is wearing No. 22 in this weekend's rookie minicamp.
The Steelers signed 4th round pick Alameda Ta'amu earlier Sunday as well.