The Endlang under 21 international has been hailed as a 'big scoop' by Latics manager Uwe Rosler who is delighted with the capture.
Speaking about McEachran to the club's official website, Rosler said: “This is a big scoop or us. There’s no doubt Josh is a huge young talent, and we have worked really hard to convince him and Chelsea this is the right place for him to be for the rest of the season.
McEachran was on loan with Watford at the start of this season and made seven appearances for the Hornets whilst he played 38 games for Middlesbrough during a loan spell last season.
With 13 caps for the Endlgand under 21's the 20 year is available for selection against Crystal Palace in the FA Cup on Saturday.
In outgoing transfer news Fraser Fyvie has joined Shrewsbury on a one month loan deal, and Jordon Mustoe has joined Wycombe Wanderers, also on a one month deal, whilst Rob Kiernan is today expected to join Roslers former club Brentford on loan until the end of the season.
Ivan Ramis has been linked with a move to Saturfay's opponents Crystal Palace, and also Ole Gunnar Solksjaer's Cardiff City whilst James McArthur is being linked with a move to Everton to team up with former Latics boss Roberto Martinez.
The Latics are still looking to make additions in the transfer window with Rosler particularly targetting a defender.