Lio Messi,29, appealed over tax fraud verdict levelled against him and his father, Jorge.
In addition to the prison term, Messi’s father, Jorge, was fined €1.5m for defrauding Spain of €4.1m in 2007-09.
However, neither man is expected to serve time in jail.
Under the Spanish legal system, prison terms of under two years can be served under probation.
The pair also face millions of euros in fines for using tax havens in Belize and Uruguay to conceal earnings from image rights.
“The sentence is not correct and we are confident the appeal will show the defence was right,” Messi’s lawyers said in a statement several hours after the guilty verdict was delivered.
The lawyers said that “there is a good chance that the appeal will succeed”, adding that Messi had always acted in good faith.
The sentence can be appealed against via the Spanish supreme court.
The footballer and his father were found guilty of three counts of tax fraud.
As well as the jail terms, Messi and Jorge were also fined. They made a voluntary €5m “corrective payment”, equal to the alleged unpaid tax plus interest, in August 2013.
Messi earns an estimated €36m per year at Barcelona, and his income of about €315m in the past decade has placed him 10th of Forbes magazine’s list of the highest-earning athletes in the world.
FC Barcelona’s reaction
“FC Barcelona expresses its full support to Leo Messi and his father in relation to the conviction for tax fraud…
“The club… considers that the player, who has corrected his position with the Spanish tax office, is in no way criminally responsible with regards to the facts underlined in this case.”