It was announced in December that a deal had been reached to keep him at the Camp Nou - and that will be signed later this week.
A club statement read: "On Thursday, the striker, who is currently in Sweden with the Argentina national team, will sign a renewed contract that binds him to FC Barcelona until June 30, 2018.
"The venue will be the club offices, and the time will be 16.30 (15.30 UK time)."
Messi scored an incredible 92 goals in 2012 and is widely considered to be one of the greatest players of all time at the age of only 25.
He already has 34 goals in La Liga this season, netting in each of his last 12 league games, and has set a number of club scoring records.
Winning a fourth World Player of the Year award in January, he has been top scorer in the Champions League for four years in a row and has won that trophy three times alongside five domestic titles and two Copa del Reys.
Barca were held by Valencia at the weekend, but hold a nine-point lead over Atletico Madrid at the top of La Liga while hated rivals Real Madrid in third are 16 points off their pace.