In a statement, Barca said that Aguero will become their player once his contract with Manchester City expires at the end of next month, adding that there is a buy-out clause “set at 100 million euros ($122 million)”.
Aguero will be unveiled as a Barca player later on Monday, signing the contract before being presented on the Camp Nou pitch.
The 32-year-old’s signing for Barca comes two days after he missed out on winning the Champions League with City, Pep Guardiola’s side losing this season’s final to Chelsea.
His final appearance for City was as a substitute for Raheem Sterling late in the final in Porto as the newly-crowned Premier League champions tried in vain to win Europe’s top prize for the first time.
He leaves City as their all-time record goalscorer with 260 goals, and with the most goals scored for a single club in Premier League history — 184 goals in 275 appearances.
His move to Barcelona had been long in the offing, with Guardiola saying a week ago that he was close to a deal with the Catalan giants.
Aguero returns to Spain after spending five years with Atletico Madrid between 2006 and 2011, during which time he won the 2010 Europa League.
Barca will hope his arrival in Catalonia helps to convince his friend and fellow Argentine Lionel Messi to stay, as the club faces up to declining performances on the pitch and a worrying financial situation.
Ronald Koeman’s side finished third in La Liga this past season and have debts of 1.2 billion euros ($1.46 billion).
They were knocked out of the Champions League at the last-16 stage by Paris Saint-Germain, and could yet face sanctions from UEFA for refusing to back out of the short-lived European Super League project.
Barca captain Messi, whose contract expires at the end of June, is yet to sign a new deal, although on Friday club president Joan Laporta said that talks for Messi’s new contract were “going well”.
“It is not done yet and we have to continue so that it gets done,” said Laporta, who added Messi staying at Barca was “not about money”.
“It’s about building a team with the possibility of winning everything. He wants Barca to think big,” he said.
Aguero will participate in this year’s Copa America, which on Monday was moved from Colombia and his home country Argentina to Brazil.