Carroll has been identified as an emergency option, with Reading suffering a number of injuries to strikers Lucas Joao and Yakou Meite.
The 32-year-old had been without a club since leaving Newcastle United at the end of last season.
"This is a deal which we have been working on for some time and are confident it is the right move for both player and club," Reading manager Veljko Paunovic told the club website.
"Andy is looking for a new challenge in his career and we need a player with his quality and vast experience.
"So this is a great match and I'm really looking forward to working with Andy over the next couple of months."
Carroll was once Liverpool’s most expensive player when he signed for £35m from Newcastle in the winter of 2011 but his time at Anfield was blighted by injuries and he was shipped out to West Ham United after his first full season.
Carroll won nine caps for England between 2010 and 2012, scoring two goals.
He could make his debut for Reading in the championship against Nottingham Forest on Saturday.
Reading are 16th on the table after 17 games.
