The Primera Division leaders recently already reached an agreement with their star player, and the attacker will put pen to paper later this week
The Argentine's current deal had been set to expire in 2016, but Catalans had already reached an agreement with the Argentine over a two-year extension in December 2012, and the prolific attacker will put pen to paper later this week.
Messi will reportedly earn an annual salary of €11 million after taxes, while he has a €250m buy-out clause in his new deal.
The 25-year-old is the third key player to sign a contract extension with Barca in 2013 after previous new deals for captain Carles Puyol and vice-captain Xavi.
Messi has made over 350 official appearances for Barcelona since making his official debut in 2004-05, netting nearly 300 goals in the process.