Song still had two years left on his contract with the Gunners, but the 24-year-old wished to move on from the team that raised him since 2005. During his time at Emirates, Song appeared in over 200 matches including 34 in the Premier League last season.
"Song will sign for the next five seasons with a release clause of €80 million," Barca announced on Twitter. "On Monday he'll have a medical and then join the rest of the squad for the official team presentation at the Gamper."
The Cameroonian joins Camp Nou as they make a run to reclaim the La Liga championship in 2012-13 season.
This has been a difficult week for Gunners fans, as Song follows the departure of superstar Robin van Persie, who transferred to Premier League rival Manchester United. Arsenal manger Arsene Wenger still feels confident about the club's midfield depth.
"It is always both [the club and player who decides]," Wenger told The Telegraph. "He had expressed a desire to go to Barcelona. In midfield we have plenty of players at the moment. You can count Diaby, Ramsey, Arteta, Cazorla, Rosicky and Coquelin, with Frimpong and Wilshere coming back. We have nine or 10 midfielders."