The 19-year-old has struggled to hold down a first-team berth since making his breakthrough at Stamford Bridge two years ago.
He will now spend the campaign with Tony Mowbray's side, who finished seventh in the Championship last season, just missing out on the play-offs.
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The highly-rated Englishman spent half of last season away from the west London club after being loaned out to Swansea, but went on to make just four appearances for the Welsh side.
His Chelsea debut came in a 2010 Champions League clash with MSK Zilina and he has since made 22 appearances in total for the Blues.
McEachran helped England to victory in the 2010 European Under-17 Championship and made his debut for the Under-21 side at just 17.