The Spanish club announced on December 18 that Messi would be extending his current deal, which expires in June 2016, by two years.
It was also announced that day that new contracts would be signed by Carles Puyol and Xavi Hernandez and that pair have already put pen to paper.
Messi, whose new contract will keep him at Barcelona until June 30 2018, is currently in Sweden with the Argentina national team.
The 25-year-old has won five league titles, three Champions League crowns, two Copa Del Rey titles and two FIFA Club World Cups since joining Barca as a youngster in 2000.
Messi won a record-breaking fourth consecutive FIFA Ballon d'Or last month after breaking Gerd Muller's 40-year-old record of 85 goals in a calendar year by scoring an incredible 91 times in 2012.