The 20-year-old follows Danny Ward from Anfield to the Scottish Premiership, the goalkeeper having been with the Dons since the start of the season.
Aberdeen manager Derek McInnes told the club website: "He's a player who has always impressed us and will give us good options in the months ahead."
The Northern Ireland international joined Liverpool from Glenavon aged 16.
He has yet to make his competitive debut for the Premier League side but made nine appearances while on loan to Barnsley in the Championship in the second half of the 2013-14 season.
That led to the first of three international caps and his only senior appearance last season was in a 1-0 friendly defeat by Scotland.
"Ryan has the quality needed to play with us at Aberdeen and we are looking forward to working closely with him," added McInnes.
"Ryan's eagerness to join us over others also give us great encouragement."
McLaughlin's older brother, Conor, is also a right-back, with League One club Fleetwood Town, and has six Northern Ireland caps.
Liverpool right-back Ryan McLaughlin has joined Aberdeen on loan until January.